Google Groups vs Usenet
It seems that a brief spell of spamming in a usenet group can cause its entire archive on Google Groups to be blocked without any way to get it unblocked. comp.sys.sinclair which was set up in 1993 is such a group.
Back in ~2001, Google took over the old Deja News archive of usenet and integrated it into Google Groups. Google Groups allows anyone to set up a group and if it gets blocked, the owner of the group has to delete any offending articles and request the group's reinstatement.
Unfortunately Usenet newsgroups don't have any owners and unless they're moderated, no way of deleting content. comp.sys.sinclar isn't moderated and as there's no owner, there's no way to get it reinstated. So there goes almost 25 years of posts!