Overkill had this version of It's Payday on the animated series website for a little bit, turns out this version dates back to 2015 and the differences are as follows:
the lyrics are slightly different in some parts, the track is a higher quality than the 2018 version (just listen to both versions and you'll instantly hear the difference in clarity), and the Payday chant is replaced by Simon saying "PAYDAY!" instead.

GeneralMcBadass actually uploaded the beta version onto his channel (I don't know if he realizes that)

I honestly like this version better than the 2018 one due to the difference in clarity, install into mod_overrides and enjoy.