Autopuzzles is a bit of fun, not a competition. The puzzles remain the "property" of the puzzle-setter as they progress through the ranks, and personally I see no harm if the OP decides to alter the answers required, especially if it reaches Pro level. Once a member has traced the origins of a car, it shouldn't take too much work to find out a bit more about the vehicle. I don't see what fun there is to be had in identifying a common mass-produced car in seconds flat - there needs to be a degree of difficulty.
I have made mistakes in the past in my puzzles, incorrectly identifying cars or believing incorrect information on the internet. It happens, and the more prolific the number of puzzles set, the more chance there is of this happening. It's frustrating for the puzzler, but we're all human. Anyone on AP who doesn't usually provide puzzles will soon learn this if they start posting their own.
(PS Mogul's post was not available when I was compiling my own reply!)