I know they go bad if left in bad condition but if there painted well then surely they won't turn to dust as they are sealed from air /road salt so on , but then again all try's to turn back to it's natural state in the end , which I think has got something to do with lime ( done it a college 17 years lol) , but Motorsport stuff normally has a shelf life cause they can ( they have a fair bit of cash to play with) but I am also sure my mates gt3 didn't come with a disclaim say after x amount of years your wheels are fit for the bin. Lol. Buying mag wheels have never bothered me as my mate works at a place where they test material and X-ray them so I would just get them checked there , peice of mind all round