There is a master list (possibly two) that everyone follows. The part that each person has to figure out is where they are in that master list. Each day that passes produces 6 new cars (hextet) in the UCD.
In order to find where you are on the list requires a bit of searching. If you post the top six or so cars that are in your UCD right now it isn't too difficult to figure out. Be sure that you post keeping the order preserved (make it look like the game).
Right doing a bit of research, and following your rules, I noticed I have the master list that FESTA has produced but with slllightly bizzarre changes to it :/, Am I placing the list in the correct order?
Here are the numbers i had: (these are 3 days in my list you can see, in descending order, so current Day first, day previous, then the day previous before that ... or Day, Day - 1, Day - 2)
3000GT MR (J) '95 FORD GT (NO STRIPE) '05
PENNOZOIL NISMO GT-R '99 STRATOS Rally Car '77
SC430 (US) '01 147 GTA '02
400R '96 CIVIC SiR-II (EG) '93
CLK-GTR Race Car '98 S2000 (EU) '03
TUSCANI CCS '03 CORVETTE C5-R (C5) '00
CUBE X '98 LEGACY B4 2.0GT '03
240SX (S14) '96 SKYLINE SEDAN 300GT '01
LEGACY B4 3.0R '03 CALSONIC SKYLINE '00
Right looking at those 3 days doesnt take a genius to work out, that, if you look, at FESTA's MasterList, im at 786/787 on the Day column, first on the left. Trouble is, I'm not sure whether I'm working it outright, but my cars are ever so slightly off from festas and placed in a different order, and 1 or 2 cars appearing in the list where they havent for me. Am I doing something wrong in my methods? I need some help please with this if possible

???
Also, looking at my day 787... My car placement method is the first of its kind it seems, as it CAN follow festas method more accurately it seems if i placed the cars in THIS ORDER:
6 1
5 2
4 3
You can see this if you start at 147GT '02 (1) and work down on my list to the S2000' (EU) 03 (3), then go directly left to the CLK-GTR Race Car '98 (4) and up to SC430 (US) '01 (6). Mind you, it doesnt work for other parts of the same code near this, in comparison to Festas :S. Is this a brand new placement order or has this been seen before?? Or am I reading festas master list wrong?
Any help would be appreciated,
Many thanks.
Mark