Calen
Skeletron Prime
This is also why the manual backup (copy to another folder periodically) is a great thing. This is something PC players have always had - and is a best practice, really, for any important files... be they Terraria files or not. Personally, I have local and icloud backups of all of my Terraria mobile players and characters of note. I update them every week. Copy - Paste - Overwrite = yes and done. Those are not subject to any issues around a .bak failing to load, etc... as they are full copies at that point in time. Thus, worst-case, you lose some progress and not everything.
If, as you said, it corrupted pre-1.3... afraid nothing can be done there, sorry.
If your a Linux user, you could always automate the process with rsync. I assume there is a Win equivalent as well.