Should be in most cases fixable through the game as well. E. g. when loading, have a check whether "wrongly_spelled_flag" is set then set "correct_spelling" and delete the other. However, that adds some code which will rarely be needed and may cause problems of its own down the way when you forget about it.
I didn't mention error correcting code as my goal was to give a simple example of how easy it is to break savegames if you aren't careful. It was a response to questioning the risk of savegames being broken in the first place and that risk is indeed real.
The issue can easily be more complex than that. Say flag A failed to increase from 4 to 5. You can't correct it by just looking for A being 4 as that is a valid value. You would have to do something like if A is 4, B greater than 7 and C greater than 3, then set A to 5. That should fix it, but what if the scene setting A to 5 also sets C to 4. Is it possible to save between setting C and setting A? Setting A to 5 when it is 5 should be fine, but what if the code says "A = A + 1". Now A is suddenly 6 when it should be 5. To get around this issue, we can run the correction code on new day event rather than on savegame load. That way we know it's not in the middle of the scene, but then....
My point is that broken savegames can likely be fixed given enough effort, but it requires development time and somebody to think through what can go wrong and counter it. This time is taken from creating new content so it might not be the best use of the time. That is unless somebody will do it and wouldn't do anything else either way.
There is also the risk that something changes and instead of C greater than 3, it should become C greater than 4, but the correction code isn't updated and then A is incorrect again. In this scenario the error correcting code broke an otherwise working savegame. This is a strong argument for not making complex error fixes and just accept that beta releases comes with some risk and players should make savegame backups or accept that they might break their save and have to start over.
It should be added that this is not strictly a beta only issue. It's just more likely with the beta as it's less tested.