Personally don’t care much for the UCD, would rather have all cars available in a normal shop with 0 km (realism be damned in this instance, everything ain’t perfectly realistic anyway), even if that’s illogical in some sense.
After all, GT tracks how many kilometres/miles you’ve driven and I do think that’s a very fun and interesting statistic. When it starts off at 30,668 km as the Corvette ZR-1 (C4) ’90 in the screenshot above I’d have to manually keep track of the distance I’ve run with it since acquiring it, despite the game having a built-in mechanism tracking distance driven. To me this is stupid.
A solution could be a separate statistic yet to be seen that tracks the distance you’ve covered in the car, despite it having heavy mileage since before. I seriously doubt that’s in the game though.