I've been storing vintage like that for years, and haven't noticed any adverse impact on the cards. You do want to make sure that they are arranged firmly, not tightly. If you have a shelf which can hold, say, 10 albums, but only have 6, you should place something against them so they stand straight up as if there were 10 - otherwise you may see them droop a bit which MIGHT lead to some warping or worse.
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