Damn the unofficial collection is so detailed, it's cool.
I just got to the page where John reaches into the homestuck thing and then you see his arm everywhere throughout the comic.
Naturally I immediately go back to those old pages and see if it's there, and it is.
That seems crazy so I wonder if they must have been added that day alongside the update, though still believing I could have just missed them.
So next I search for an old thread to see reactions: https://desuarchive.org/co/thread/48088700/#48089017
Clearly they weren't there before on the real site, but does that mean I really just never noticed them?
So I go back to UHC and change my new reader progress back a few pages and refresh the old pages and the arms are now gone, they actually accounted for that. I just checked the current mirror sites kici and chadthundercock and they always have the armed versions of those pages.