Are you not keeping the Itch.io version up to date? The Steam version is up to .121 now. But the version listed here is .117.
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I did get a response from the developer over at the Steam forums. Apparently the version numbers itch.io use don't match up to the ones Steam is using, but the game is in fact up-to-date here on itch. I can confirm this is the case as the in-game version number on my purchased itch.io install is indeed the latest!