Alternate Earth U.N.C.L.E. Agents

First time watching the pilot for THE GIRL FROM U.N.C.L.E. in decades. I remembered that Mary Ann Mobley preceded Stefanie Powers as a very different, more sophisticated April Dancer but I had totally forgotten that Norman Fell, of all people, was the original Mark Slate! It's even said he had mentored Napolean Solo years earlier. April comments that U.N.C.L.E. regulations require agents of his age to have a desk job. Age jabs occur throughout. Perhaps the later Slate as played by Noel Harrison is this one's (English) son? Who knows? It's never said.