Defiant Explorer regarding a bit in the latest Patreon post...
There is another, simpler way this sort of thing can be resolved, that would alleviate all such problems going forward. This is done by adding a special function to your game, which checks the save files when they're loaded, and if it finds the save is from older version of the game it can correct/add any variables which have been added or changed between the game releases.
You can find exact instructions how to do it and complete code ready for copy/paste, together with some sample use,
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(the alternative approach you've come up with should work, too. but this one is something to keep on mind since it's more generic)