Some famous examples of vintage cards going down:
2016 "Buyers Group" really shilled up the prices of 1950s and 1960s Hall of Fame level rookies in PSA 7,8,9 grades (Clemente, Rose, Koufax, etc) to double, triple, or quadruple their original prices in only a few months. After they stopped buying, cards dropped again. This would be considered a market bubble that burst.
If you search the Auction Prices Realized website for PSA graded cards, take a look at the 1952 Topps set. Many PSA 8 cards sold early on for like $10K each, and the same exact cards (cert numbers) sold just a few years later in many cases for a fraction of those prices (down in the $1-2K range). Not sure if once the top buyers got their cards, the demand decreased, or whether the supply kept growing and now the whales needed PSA 9/10s to remain competitive.
https://www.net54baseball.com/showth...light=realized
Pre-war has probably had sets go out of favor and dropped because of that. Most of the candy/food cards had a resurgence like 10 years ago, and have probably been flat to down since then.