Chris Khalaf told me back in 1991 that Maitz had supposedly done work as an assistant to Jim Aparo in the 70s. When Chris and I met Jim for the first time in 1992, we asked him about this rumor.
Jim confirmed that he knew Maitz, and that Maitz had visited his studio when Maitz was a greenhorn, but quite strongly declared that Maitz had never served as an assistant. According to Jim, the only person that ever touched his art (other than meddlers at DC that very occasionally fiddled with what he turned in) was his wife, who occasionally wielded a brush to fill in blacks. I couldn't resist telling him about Dave Sim's comments about how he had allowed his wife to do the same on some early issues of Cerebus, with disappointing results. I told him how it was plainly obvious which pages Sim's wife had "blacked", and he was a little bit flabbergasted at my insistence that, yes, having a non-artist spot blacks could yield very bad results. Maybe Jim was just better at specifying black spots in the pencil art than the young Sim was, because I couldn't begin to guess on which pages Julieann Aparo splashed ink.
And yes, Jim Aparo knew very well who Dave Sim was...I was quite surprised to learn how familiar he was with all of the talents working in the burgeoning comics business of the 80s and 90s. He was certainly not out of touch with the new blood that was expanding the boundaries of comics. Jim was a sharp fellow, who paid close attention to the art form.