just about any NES game i physically owned on a real NES lost it's saves, yep i held the reset button as i turned it off, didn't matter.
so i had to play most NES games in one sitting, zelda 1 for example. i never finished it the console would "reset" itself eventually.
in later times, i had my dreamcast main memory card die, stopped working entirely. lost all my progress of sonic adventure (100% of all missions) sonic adventure 2 (all but like 2 A ranks left) sonic shuffle (stupid amount of time to unlock everything on there) rush 2049 (so many time records), marvel vs capcom 2, power stone 1 and 2, capcom vs snk,SF alpha 3, gauntlet legends, crazy taxi, hydro thunder, crazy taxi 1 and 2 all those side missions, the one that made me mad the MOST, tony hawks pro skater 2, I did everyone to 100% all the characters! no cheats! thats a LOT of time. plus more games i can't remember i had a lot of them.
so i did the logical thing, bought a gameshark and basically blasted through all those games again, cause no way in hell was i playing all of those all over again.
also had about 6 memory cards after that and made copies on multiple cards. never had another memory card break or go corrupt after that one time though lol just my luck.
on my emulators i've lost saves many many times to where its just oh well, or i use cheats to catch up (i don't cheat normally on any game, ONLY if i'm replaying or lost save data or its an incredibly hard game)
my PS4 completely had to reformat the system corrupted entirely, i don't have PS plus, and never have, so i lost about 200 games save data in one moment. i made "some" USB backups but that was extremely longer games like disgaea (100 hours on every single one at least, 350 on Disgaea 4) and persona games. and wasn't recent. it was painful but i'm too old to care and it gave me an excuse to replay some games.