Don Herron has news that Derleth scholar John D. Haefele has…

the first comprehensive checklist of Arkham House ephemera, Modern Era, ever published [in the] September/October 2019 issue of Firsts: The Book Collectors Magazine.

Ah, but this is only the prelude. “Now You’ll Need Two Issues” added Don a few days later. September/October carries the introductory essay, with the actual list in the following issue.