Been reading the L. Sprague Decamp/Lin Carter short stories in Conan the Swordsman this week. Seems to me that these later Conan pastiches are somewhat better written than the ones which appeared in the Lancer Conan books in the 1960s. Don't know if that means more editing by Decamp to Carter's first drafts or less, of if both writers had benefited from the time between their last take on Conan and this. (Decamp and Carter wrote a few more Conan pastiches in the early 70s as well.) A lot of Robert E. Howard fans absolutely hate the Decamp/Carter pastiches, but I've only recently read them and haven't found them to be that bad. A couple have been very enjoyable in fact.
According to Decamp, in his autobiography Time and Chance, the process for his collaborations with Lin Carter was for Carter to write the first draft of the story and Decamp to do the second. This was a reversal of the process Decamp had used when collaborating on the Harold Shea stories with Fletcher Pratt. Decamp felt that the more seasoned writer should do the final draft. Decamp noted that he rewrote some of Carter's stories quite extensively, and only edited others. Unfortunately there's no good record of what was done to what story. I'd find that interesting.
The Gem in the Tower has been my favorite story in Swordsman, and it may be a sequel to the REH non Conan tale, The Garden of Fear. There is a winged man in a tower which has no doors or windows except at the top as in Garden, and the text indicates he's from some ancient alien race, which would also tie in. But the physical description of the winged man differs somewhat from the one in Garden so I can't say for sure that Decamp/Carter meant him to be of the same species. May have just been a tip of the hat.
The Ivory Goddess is a direct sequel to Jewels of Gwahlur and picks up just a couple of weeks after that story. It even manages to tie up a couple of loose ends from Jewels. Moon of Blood is also a sequel, this time to Beyond the Black River, and it may be the story in the book that comes closest to feeling like an actual REH tale. Sprague and Lin rose to the occasion of writing a 'frontier' Conan yarn quite admirably.
Swordsman came out in 1978, and all the Decamp/Carter stories seem to have been written specifically for the book with no prior magazine publications. There are also two Decamp collaborations with Bjorn Nyberg, one of which is a rewrite of Nyberg's The People of the Summit which appeared in the anthology The Mighty Swordsmen. I've found Nyberg's other Conan work to be all but unreadable, so I've skipped those