Can’t be any of the ones listed. Robinson said “two dozen sequels”. Even if he was speaking loosely, there were only one or two SF/F series that IN 1982 (or so…I don’t remember the original publication date of Callahan’s) had 20-some sequels.
Remember, in the actual quote, Robinson says he won’t name the author because he’s worried that the author’s estate will come after him.
So, we need to narrow the list even further: a series that, in the early '80s had 20+ books and where the author was dead.
Gor, in 1982 was around book 12,
Xanth was at about 7 and wasn’t horrible yet (it wasn’t good or anything. but it wasn’t horrible),
Burrough’s Tarzan was at 24 (but IIRC Robinson expressed admiration for Burroughs in some interview or other).
E.C. Tubb had a long series back then, but was still alive
Marion Zimmer Bradley’s Darkover stuff was approaching the 20s, but again she was alive and at the time her stuff was very respected (Heritage of Hastur, Forbidden Tower)
The only thing I came up with the last time this came around was Edmund Hamilton’s CAPTAIN FUTURE series. 20 books, never reprinted (never a good sign), Hamilton was dead by the time Callahan’s was published. It fits all the points, but I dunno.
Ah-ha. This did come up before
I’d swear there was another discussion about this though, and (IIRC) someone who actually knew Robinson said that the story was a to illustrate a point. I’ve come to that conclusion myself. There really aren’t any books that fit the facts in evidence.
Frankly, I’ve come to the conclusion that Robinson made up a story to illustrate a point.
Fenris