I'm sure the PD releases would make at least some impact. I think most here would agree that the PD releases of One Step Beyond had a definite negative impact on sales of the cleaned-up, remastered Season One set, enough so that Paramount didn't see any reason for remastering/releasing the rest.
Technically, Project: UFO is a two-season show, although it only amounts to two runs of 13 (the equivalent of most single-season shows back then).
I think the hold-up with that show has something to do with rights/ownership, doesn't it (Mark VII Productions)?