@apLundell Well, we don't really know (and I suppose it doesn't matter for plot purposes), but my best guess is that that one was his actual car but after the apocalypse he "adopted" a bunch of other cars whose owners had been turned to dust. That is, when he says "I have 23" he just means 23 cars, not necessarily 23 new convertibles.
Or he doesn't have any other cars but he's just making something up to impress Samantha, and maybe he realizes it'll be easy to find 23 cars he can claim to own.
#Monsterdon