I see references to John Gilmore being the original author of pdtar, and John Gilmore using the gnu handle, but I don't see any references to his usage of the name predating the GNU project or pdtar being referred to as gnutar before it became part of the GNU project.

I'm not saying that I disbelieve you, I just haven't been able to find any references for your claim.

ChangeLog.1 and NEWS only go back to after it was migrated to the GNU project (http://git.savannah.gnu.org/gitweb/?p=tar.git;a=tree), his personal site, http://www.toad.com/gnu/ seems to be down but an archive (https://web.archive.org/web/20180623140434/http://www.toad.c...) just says 'In 1985 I wrote the "pdtar" program, which eventually became GNU Tar.'

He clearly uses the name "gnu", but did that usage predate the GNU project? I haven't found a reference for that.