There is a grey area when, say, a front view gets solved and later someone posts a 3/4 rear view. It may not be immediately apparent that it is in fact a repost. In this case I think the puzzle should be allowed to run its course and then merged as a repost.
As the total of solved puzzles approaches 9000, we are slowly approaching a situation where the only cars left are obscure one-off unbult prototypes, racing specials, hot rods and custom cars. When this is reached either the forum will stagnate with nobody but the pros being knowledgeable enough to solve anything posted or we will have to formulate a policy to allow reposts. This could be as simple as saying "When there is a repost, anybody who posted on the original puzzle may not post on this one." It won't fully solve the problem but will do so partially.