Homologation is the reason many of my favorite cars exist. Lancia Delta Integrale, Lancia Stratos, Lancia Delta S4 Stradale, Lancia 037 Stradale, BMW M3 GTR, Ford RS200, Audi Sport Quattro, Escort Cossie, or the 22B, just to name a few.
The 22b was sort of done in reverse. It was a commemorative car that was based off of the shape of the rally car at the time, the Impreza WRC99. The wide blistered fender flares were an homage to the rally cars shape, not the result of requirements for homologation.
In the 99 season, the Impreza had just switched to the, then new, WRcar class from the older Group-A spec (that Mitsubishi ran up to the EVO6.5), which meant that homologation specials were no longer required to make a fire breathing AWD rally car. You simply had to base it off of a high volume production model. The Impreza WRC99 and WRC2000, if memory serves me right, were based off of a European base model Impreza which came only in FWD, a pure economy model. Using this car as the homologation base, allowed Prodrive to change the pick up points and geometry of the rear suspension, over that of the AWD road cars, which was something that was a constant source of headache in the Impreza Group-A cars, be it form lack of travel, or geometry compromises. Either way, the move was a nice way to use the rules to make the cars competitive evolution move along, without having to release a new road car to match Mitsubishi's latest Evolution of the Lancer, a car that had trumped the Group-A formula in a way only rivaled by Lancia before them.
The Group-B homologation rules required 200 cars. It is believed that most of the manufactures either lied outright to the FIA about the numbers built, or made 200 cars "in part", simply to appease the FIA. There is even a great story of Jean Todt (yes that Jean Todt), who was the team director at Peugeot at the time of the 205 T16 program, walking FIA officials around the Peugeot factory showing them "all" the 205's they had built for homologation. They would show them one warehouse full of T16's then go take a factory tour, have some cheese and wine, then suddenly "over here in this warehouse we have yet MORE 205 T16's!" Followed by some more sight seeing, and wine. Rumor also has it that the majority of the "cars" in the warehouses were simply the fiberglass body panels on chassis jigs, with only the first 10-15 cars in the front actually being built, functional, complete cars. This shell game of "move the 205's" continued for the better part of the day, until the FIA officials were good and bored, as well as heavily inebriated, and finally signed off on the homologation papers with little complaint. You will note that there is no glut of 205 T16 road cars for sale, because they never exsisted.
The Group-A homologation cars were a differnt story all together. With many manufactures not only making special road going models (Lanver Evolution, WRX STi, Escort Cosworth, Celica GT-4, etc.) to qualify for Homologation, but also making special models of those models. The FIA reffered to these officially as "evolutionize" models. So while the Toyota Celica ST-185 was the homologated car, they would build a special "RC" model, which would have bigger radiators, beefier pumps, beefier suspension pickup points, etc. In some cases even the engines would be modified, either with billet internals, or fully closed decks, oil squirters, dog ring transmissions, etc. It was, in effect, a partly prepped racing build. This allowed for greater freedom within the rules for modification, as they could point to these cars and say "yes, see, we produced that in mass for homologation, of course that machined bespoke part is production based". It also meant that when factory efforts would occasionally support Group-N production based programs, they could send one of these "evolutionize" cars to the event to help improve the brands chances of winning. This is largely why, in their heyday, Mitsubishi and Toyota dominated their Group-N fields for as long as they did, especially Mitsubi****.
Occasionally one of these cars would get sold to someone they wherent supposed to, and turn up on a grey market importer somwhere. For example i know someone with a Group-A Mazda BP turbo motor out of a 323 GTX, and a 3SGTE out of a Celica ST-185 RC. In both cases, these motors internally are completely different than their production counterparts. THe Mazda is currently making 500 BHP in an Escort, and the Celica motor is in an ST-165, making about 360BHP, and a whopping 480 lbs. ft. of torque. There is no way you could do that with either of those motors stock, even with them being heavily modified from stock. These are racing both pure racing engines, of which the comparison with stock ends at the external dimensions of the block.
OK, I've rambled enough...
And the rarity, the fact that they are basically myths. Wish there were more in the GT series, but the R390, Stratos and such will do 👍
