I always wondered if Glen Cook's Garrett PI was given that name as a nod of the head to Randall Garrett. Before the Urban Fantasy trend Lord D'Arcy and Garrett PI were the best known (at least to me) investigators in worlds where magic is prevalent.
Yep, Randall Garrett and Michael Kurland, and other Sci-Fi, Fantasy and Detective writers who knew and liked each others' works would work the other authors' names and characters into the stories. In one of David Weber's
Honor Harrington sci-fi stories, in the far distant future, one of the characters is reading an ancient Earth detective story featuring "Garrett Randall, P.I.".