Gordon Hutching, in his Book of Pyro recommended saving spent PMK developer to use as an "afterbath" for soaking your developed and fixed PMK films in to increase the strength of the pyro stain on the negatives. I first used PMK in the early 90s, and I followed his suggestion. To me, it initially seemed counter intuitive, but I did it as it was in the Book, and so I did it religiously.
He later retracted that, all that happens is an overall base stain is added, it's not a benefit and if patchy highly detrimental. So you did the right thing (in your next paragraph)