I accidentally updated, but my replays are still there - why?

Solution 1:

It's been awhile since I've been home to play Smash on my own Switch, but I finally got the chance last night.

Upon opening Smash, I was prompted with the screen below with some Version 3.1.0 details. I've highlighted one bullet in particular (the system wouldn't let me screenshot this, so enjoy a picture of my TV):

• There may be some compatibility issues with replays from Ver. 3.0.0 and Ver. 3.0.1. Replays from Ver. 2.0.2 and earlier are not compatible. If you want to keep your replays, convert them into videos before installing the update. You can do this via Vault -> Replays -> Replay Data -> Convert to Video.

It sounds like Nintendo only "invalidated" replays from 2.0.2 and earlier (the last update before 3). 3.0.0 updates on the other hand, they've left with a warning that "there may be some compatibility issues."

It looks like these "compatibility issues" are exactly what you're seeing--but at least you didn't lose all of your replays this time!