> Is anyone aware of either of the following, then:
> 1. A USENET corpus that goes back 15-20 years (beyond what's available
> at Google Groups), or
With the exception of material excluded via the obsolete X-Archive: header (and the really dubious content of various newsgroups in the alt heirarchy) Google Groups archive of UseNet news is pretty much complete. They acquired the old DejaNews archive when that organisation went bust. DejaNews was *the* UseNet news archive at the time. I don't recall any other archive existing from that era. If there was it was not widely known. So Google Groups is probably what you'll have to work with.
<>< Re: deemed!