[2021] Question About Previous Betas

Your characters and progress are specific to the specific save it is from (including server progress), and saves are non compatible between major versions; If you went back to say, A16, You likely wouldn't even be able to see your saves in the menu, let alone actually load them. So you should be good to go.

Originally posted by Plato: Another question here...

If I go install 15.2, it's showing 1.2GB download. When I go back to 19.3, will I have to re-download this version, or they will both stay on my machine along side one another?

Former. If you want both versions, you'll have to copy the game folder in it's entirety then install the second. (And in this case it'd be best to install the earlier version, copy that to a new location, then update back to latest- As the older version is unchanging while the new one will have updates.)