Agree with what Luke and Ken said -- scrap books, shoe boxes, etc.
I think
that, say cards that were produced in 1910, that are high grade today were high grade in 1915. Those were the ones NOT "played" with. The cards that are low grade today, again, were low grade by 1915. Those were the ones traded, shoved in pockets, went through the wash, etc., etc.
Although I mainly deal with lower to mid grade cards, I have handled a few higher grade ones. These cards are actually, imo, quite durable little pieces of card board. You would have to blatantly fold them in half to get a crease, or bang them very hard to mess up a corner. Conversely, once a "handled" card is wrinkled, a wrinkle can turn into a crease with more handling, as well as a corner ding turn into corner wear.
Well, that didn't add much.