The Save a Copy default should be to not overwrite existing copies. Instead it should append a number to the filename of the new copy, the same way MacOS handles file duplicates. Overwriting could be a checkbox in the Save a Copy dialog box.

If it worked this way, I'd have a simple method of keeping versions of my files without having to remember to rename each copy. If there's another way to do this via a script, I'm all ears! Cloud docs are unfortunately not an option for me.