As Alex McDonald notes in this
support request, Google has recently banned the old Usenet groups
comp.lang.forth and comp.lang.lisp from the Google Groups system.
"Of specific concern is the archive. These are some of the oldest
groups on Usenet, and the depth & breadth of the historical material that
has just disappeared from the internet, on two seminal programming
languages, is huge and highly damaging. These are the history and
collective memories of two communities that are being expunged, and it's
not great, since there is no other comprehensive archive after Google's
purchase of Dejanews around 20 years ago."
Perhaps Google can be convinced to restore the content, but it also seems
that some of this material could benefit from a more stable archive.