Ok well, I think it's time many years later, that this answer is stated on the internet once and for all. 9.5 years later I will attempt to answer my younger self, with help from Kudos Prime.
1111 cars initially let's see how many are duplicated.
The rules? I will completely make them up, and I will list all of the cars I deem have been duplicated.
Premium (15)
Chevrolet [INSERT RACE DRIVER LIVERY] IMPALA '10 x 4 (5 total, 4 duplicates)
Chevrolet [INSERT RACE DRIVER LIVERY] IMPALA '11 x 4 (5 total, 4 duplicates)
Ford [INSERT RACE DRIVER LIVERY] FUSION '10 x 1 (2 total, 1 duplicate)
Ford [INSERT RACE DRIVER LIVERY] FUSION '11 x 1 (2 total, 1 duplicate)
Gran Turismo Red Bull X2010 Prototype (Duplicate of Gran Turismo Red Bull X2010)
Gran Turismo Red Bull X2010 S.Vettel (Duplicate of Gran Turismo Red Bull X2010)
Mazda Eunos Roadster J-Limited (NA) '91 (Duplicate of Mazda Eunos Roadster (NA Special Package) '89, Premium)
Mazda éfini RX-7 Type R (FD) '91 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02)
Mini MINI COOPER S '05 (Duplicate of Mini MINI COOPER S '11)
Standard (136)
Acura CL 3.2 Type-S '01 (Duplicate of '03)
Aston Martin DB9 Coupe '03 (Duplicate of '06, Premium)
Autobacs ARTA Garaiya '03 (Duplicate of '08, Premium)
BMW M5 '05 (Duplicate of '08, Premium)
Chevrolet Camaro Z28 '69 (Duplicate of another '69, Premium)
Daihatsu Copen Detachable Top '02 (Duplicate of Daihatsu Copen Active Top '02)
Daihatsu SIRION X4 (J) '00 (Duplicate of Daihatsu SIRION X4 '00)
Dodge Viper GTS-R Team Oreca Race Car #51 '00 (Duplicate of Dodge Viper GTS-R Team Oreca Race Car #91 '00)
Ferrari Enzo Ferrari '02 (Duplicate of Ferrari Enzo Ferrari '02, Premium)
Ferrari F2007 (Duplicate of Ferrari F2007, Premium)
Fiat 500 F '65 (Duplicate of Fiat 500 F '68, Premium)
Ford Ford GT '02 (Duplicate of Ford GT '06, Premium)
Ford Ford GT '05 (Duplicate of Ford GT '06, Premium)
Ford Ford GT '05 (No Stripe) (Duplicate of Ford GT '06, Premium)
Honda BEAT Version F '92 (Duplicate of Honda Beat '91)
Honda BEAT Version Z '93 (Duplicate of Honda Beat '91)
Honda CIVIC SiR-II (EG) '91 (Duplicate of Honda CIVIC SiR-II (EG) '95)
Honda CIVIC SiR-II (EG) '92 (Duplicate of Honda CIVIC SiR-II (EG) '95)
Honda CIVIC SiR-II (EG) '93 (Duplicate of Honda CIVIC SiR-II (EG) '95)
Honda CIVIC TYPE R (EK) '98 (Duplicate of Honda CIVIC TYPE R (EK) '97, Premium)
Honda CIVIC TYPE R (EP, EU) '01 (Duplicate of Honda CIVIC TYPE R (EP) '01)
Honda INTEGRA TYPE R (DC2) '95 (Duplicate of Honda INTEGRA TYPE R (DC2) '99)
Honda INTEGRA TYPE R (DC2) '98 (Duplicate of Honda INTEGRA TYPE R (DC2) '99)
Honda INTEGRA TYPE R (DC5) '03 (Duplicate of Honda INTEGRA TYPE R (DC5) '04, Premium)
Honda NSX '90 (Duplicate of Honda NSX '99)
Honda NSX '93 (Duplicate of Honda NSX '99)
Honda NSX '95 (Duplicate of Honda NSX '99)
Honda NSX '97 (Duplicate of Honda NSX '99)
Honda NSX Type R '92 (Duplicate of Honda NSX Type R '92, Premium)
Honda NSX Type S '97 (Duplicate of Honda NSX Type S '99)
Honda NSX Type S Zero '97 (Duplicate of Honda NSX Type S Zero '99)
Honda PRELUDE Type S '96 (Duplicate of Honda PRELUDE Type S '98)
Honda S2000 '99 (Duplicate of Honda S2000 '06, Premium)
Honda S2000 '01 (Duplicate of Honda S2000 '06, Premium)
Honda S2000 '06 (Duplicate of Honda S2000 '06, Premium)
Honda S2000 (EU) '99 (Duplicate of Honda S2000 '06, Premium)
Honda S2000 (EU) '01 (Duplicate of Honda S2000 '06, Premium)
Honda S2000 (EU) '03 (Duplicate of Honda S2000 '06, Premium)
Honda S2000 (US) '99 (Duplicate of Honda S2000 '06, Premium)
Honda S2000 (US) '01 (Duplicate of Honda S2000 '06, Premium)
Honda S2000 (US) '03 (Duplicate of Honda S2000 '06, Premium)
Honda S2000 Type V '00 (Duplicate of Honda S2000 '06, Premium)
Honda S2000 Type V '01 (Duplicate of Honda S2000 '06, Premium)
Honda S2000 Type V '03 (Duplicate of Honda S2000 '06, Premium)
Honda S2000 Type V (EU) '00 (Duplicate of Honda S2000 '06, Premium)
Honda S2000 Type V (EU) '01 (Duplicate of Honda S2000 '06, Premium)
Honda S2000 Type V (US) '00 (Duplicate of Honda S2000 '06, Premium)
Honda S2000 Type V (US) '01 (Duplicate of Honda S2000 '06, Premium)
Infiniti G35 COUPE '03 (Duplicate of Infiniti G35 COUPE '06, Premium)
Jaguar XJR-9 LM Race Car '88 (Duplicate of Jaguar XJR-9 LM Race Car '88, Premium)
Lexus GS 300 Vertex Edition (J) '00 (Duplicate of Lexus GS 300 '00)
Lexus IS 200 (J) '98 (Duplicate of Lexus IS 200 '98)
Lexus SC 430 (EU) '01 (Duplicate of Lexus SC 430 (US) '01)
Lotus Elise 111R '04 (Duplicate of Lotus Elise 111R '04, Premium)
Lotus Esprit V8 '02 (Duplicate of Lotus Esprit V8 '02, Premium)
Lotus Esprit V8 SE '98 (Duplicate of Lotus Esprit V8 GT '98)
Mazda 110S (L10A) '67 (Duplicate of Mazda Cosmo Sport (L10A) '67)
Mazda 110S (L10B) '68 (Duplicate of Mazda Cosmo Sport (L10B) '68)
Mazda Eunos Roadster J-Limited II (NA) '93 (Duplicate of Mazda Eunos Roadster (NA Special Package) '89, Premium)
Mazda Eunos Roadster S-Special I (NA) '95 (Duplicate of Mazda Eunos Roadster (NA Special Package) '89, Premium)
Mazda Eunos Roadster SR-Limited (NA) '97 (Duplicate of Mazda Eunos Roadster (NA Special Package) '89, Premium)
Mazda Eunos Roadster V-Special II (NA) '93 (Duplicate of Mazda Eunos Roadster (NA Special Package) '89, Premium)
Mazda Eunos Roadster VR-Limited (NA) '95 (Duplicate of Mazda Eunos Roadster (NA Special Package) '89, Premium)
Mazda MX-5 (NA) '89 (Duplicate of Mazda Eunos Roadster (NA Special Package) '89, Premium)
Mazda MX-5 J-Limited (NA, J) '91 (Duplicate of Mazda Eunos Roadster (NA Special Package) '89, Premium)
Mazda MX-5 J-Limited II (NA, J) '93 (Duplicate of Mazda Eunos Roadster (NA Special Package) '89, Premium)
Mazda MX-5 Miata (NA) '89 (Duplicate of Mazda Eunos Roadster (NA Special Package) '89, Premium)
Mazda MX-5 Miata S-Special I (NA, J) '95 (Duplicate of Mazda Eunos Roadster (NA Special Package) '89, Premium)
Mazda MX-5 Miata SR-Limited (NA, J) '97 (Duplicate of Mazda Eunos Roadster (NA Special Package) '89, Premium)
Mazda MX-5 Miata V-Special II (NA, J) '93 (Duplicate of Mazda Eunos Roadster (NA Special Package) '89, Premium)
Mazda MX-5 Miata VR-Limited (NA, J) '95 (Duplicate of Mazda Eunos Roadster (NA Special Package) '89, Premium)
Mazda MX-5 S-Special I (NA, J) '95 (Duplicate of Mazda Eunos Roadster (NA Special Package) '89, Premium)
Mazda MX-5 SR-Limited (NA, J) '97 (Duplicate of Mazda Eunos Roadster (NA Special Package) '89, Premium)
Mazda MX-5 V-Special II (NA, J) '93 (Duplicate of Mazda Eunos Roadster (NA Special Package) '89, Premium)
Mazda MX-5 VR-Limited (NA, J) '95 (Duplicate of Mazda Eunos Roadster (NA Special Package) '89, Premium)
Mazda MX-5 1.8 RS (NB, J) '98 (Duplicate of Mazda MX-5 Miata 1800 RS (NB, J) '04)
Mazda MX-5 1600 NR-A (NB, J) '04 (Duplicate of Mazda MX-5 Miata 1800 RS (NB, J) '04)
Mazda MX-5 Miata 1800 RS (NB, J) '00 (Duplicate of Mazda MX-5 Miata 1800 RS (NB, J) '04)
Mazda Roadster 1.8 RS (NB) '98 (Duplicate of Mazda MX-5 Miata 1800 RS (NB, J) '04)
Mazda Roadster 1600 NR-A (NB) '04 (Duplicate of Mazda MX-5 Miata 1800 RS (NB, J) '04)
Mazda Roadster 1800 RS (NB) '00 (Duplicate of Mazda MX-5 Miata 1800 RS (NB, J) '04)
Mazda Roadster 1800 RS (NB) '04 (Duplicate of Mazda MX-5 Miata 1800 RS (NB, J) '04)
Mazda RX-7 GT-LIMITED (FC, J) '85 (Duplicate of Mazda RX-7 GT-X (FC) '90, Premium)
Mazda RX-7 GT-X (FC, J) '90 (Duplicate of Mazda RX-7 GT-X (FC) '90, Premium)
Mazda SAVANNA RX-7 GT-Limited (FC) '85 (Duplicate of Mazda RX-7 GT-X (FC) '90, Premium)
Mazda SAVANNA RX-7 INFINI III (FC) '90 (Duplicate of Mazda RX-7 GT-X (FC) '90, Premium)
Mazda RX-7 Type R (FD, J) '91 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02, Premium)
Mazda RX-7 Type R (FD, J) '93 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02, Premium)
Mazda RX-7 Type R Bathurst R (FD) '01 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02, Premium)
Mazda RX-7 Type R-S (FD, J) '95 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02, Premium)
Mazda RX-7 Type RS (FD) '00 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02, Premium)
Mazda RX-7 Type RS (FD) '98 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02, Premium)
Mazda RX-7 Type RS (FD, J) '96 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02, Premium)
Mazda RX-7 Type RS-R (FD) '97 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02, Premium)
Mazda RX-7 Type RZ (FD) '00 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02, Premium)
Mazda RX-7 Type RZ (FD, J) '92 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02, Premium)
Mazda RX-7 Type RZ (FD, J) '93 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02, Premium)
Mazda RX-7 Type RZ (FD, J) '95 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02, Premium)
Mazda RX-7 Type RZ (FD, J) '96 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02, Premium)
Mazda éfini RX-7 Type R (FD) '93 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02, Premium)
Mazda éfini RX-7 Type R-S (FD) '95 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02, Premium)
Mazda éfini RX-7 Type RS (FD) '96 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02, Premium)
Mazda éfini RX-7 Type RZ (FD) '92 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02, Premium)
Mazda éfini RX-7 Type RZ (FD) '93 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02, Premium)
Mazda éfini RX-7 Type RZ (FD) '95 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02, Premium)
Mazda éfini RX-7 Type RZ (FD) '96 (Duplicate of Mazda RX-7 Spirit R Type A (FD) '02, Premium)
Mazda RX-8 '03 (Duplicate of Mazda RX-8 Type S '07, Premium)
Mazda RX-8 Type E '03 (Duplicate of Mazda RX-8 Type S '07, Premium)
Mazda RX-8 Type S '03 (Duplicate of Mazda RX-8 Type S '07, Premium)
Mazda RX-8 Concept (Type-I) '01 (Duplicate of Mazda RX-8 Concept (Type-II) '01)
Mercedes-Benz 300 SL Coupe '54 (Duplicate of Mercedes-Benz 300 SL Coupe '54, Premium)
Mine's BNR34 SKYLINE GT-R V・spec N1 base '00 (Duplicate of Mine's BNR34 SKYLINE GT-R N1 base '06, Premium)
Mini MINI COOPER '02 (Duplicate of Mini MINI COOPER S '11, Premium)
Mini MINI COOPER S '02 (Duplicate of Mini MINI COOPER S '11, Premium)
Mini MINI ONE '02 (Duplicate of Mini MINI COOPER S '11, Premium)
Mitsubishi 3000GT SL (J) '95 (Duplicate of Mitsubishi 3000GT MR (J) '95)
Mitsubishi 3000GT SR (J) '95 (Duplicate of Mitsubishi 3000GT MR (J) '95)
Mitsubishi 3000GT SR (J) '96 (Duplicate of Mitsubishi 3000GT MR (J) '95)
Mitsubishi 3000GT SL (J) '96 (Duplicate of Mitsubishi 3000GT MR (J) '95)
Mitsubishi 3000GT SL (J) '98 (Duplicate of Mitsubishi 3000GT MR (J) '98)
Mitsubishi 3000GT SR (J) '98 (Duplicate of Mitsubishi 3000GT MR (J) '98)
Mitsubishi 3000GT VR-4 Turbo (J) '95 (Duplicate of Mitsubishi 3000GT VR-4 (J) '98)
Mitsubishi 3000GT VR-4 Turbo (J) '96 (Duplicate of Mitsubishi 3000GT VR-4 (J) '98)
Mitsubishi FTO GP Version R '97 (Duplicate of Mitsubishi FTO GP Version R '99)
Mitsubishi FTO GPX '94 (Duplicate of Mitsubishi FTO GP Version R '99)
Mitsubishi FTO GPX '97 (Duplicate of Mitsubishi FTO GP Version R '99)
Mitsubishi FTO GPX '99 (Duplicate of Mitsubishi FTO GP Version R '99)
Mitsubishi FTO GR '94 (Duplicate of Mitsubishi FTO GP Version R '99)
Mitsubishi FTO GR '97 (Duplicate of Mitsubishi FTO GP Version R '99)
Mitsubishi GTO SR '95 (Duplicate of Mitsubishi GTO SR '98)
Mitsubishi GTO SR '96 (Duplicate of Mitsubishi GTO SR '98)
Mitsubishi GTO Twin Turbo '95 (Duplicate of Mitsubishi GTO Twin Turbo MR '98)
Mitsubishi GTO Twin Turbo '96 (Duplicate of Mitsubishi GTO Twin Turbo MR '98)
Mitsubishi GTO Twin Turbo '98 (Duplicate of Mitsubishi GTO Twin Turbo MR '98)
Mitsubishi GTO Twin Turbo MR '95 (Duplicate of Mitsubishi GTO Twin Turbo MR '98)
Mitsubishi Lancer Evolution VII GSR '01 (Duplicate of Mitsubishi Lancer Evolution VII GT-A '02)
I'm going to pause here for now