Alright - figured it out.
Itch.io version of the plugin is outdated. If I click "download now" at the top of the page, go straight to downloads, and select itch.io v2, it gives me a version with a python script that is only 300-some lines of code. While directly downloading from github gives me a script that is 500-some lines of code and aligns more with the description above.
OH MY GOD. Thank you so much for not giving up! I've correct the mistake!
Sheesh, i keep former versions as I work and did not realize that I had re-uploaded a former v1 version on Itch, even though the Github had the latest. This explains so many questions i've had from users lately. Thanks so much for getting to the bottom of it for me.
I've fixed it, it should be good now, and i'll be more careful in the future!
Your welcome, be warned of the lastest 2.2.0 release. A lot of changes compared to former rigs, could mess with compatibility with older rigs But it was the tradeoff to add Unreal/Unity compatibility too, and make it the semi-official rig of the Quaternius models. (check out his stuff if you haven't already. Great great free assets, models, animations, clothes, etc.