I'd tend to think the problem lies in the fact that they were a start up company, and they probably didn't keep track of all the old paperwork. And I'm wondering if they planned to recast Gordon once the show went public anyway.
In
Street Gang, Jon Stone is quoted as saying that Saunders was cast at the last minute, and that nobody was happy with the casting, so most probably. He's not the only thing about the test pilot that's rough around the edges (Susan was almost at Vanna White-level in being 'set dressing'), and even though Matt Robinson's Gordon was more streetwise than Roscoe Orman's (I haven't seen enough of Hal Miller to comment), it is fairly clear that Saunders' character didn't have much 'Gordon' about him.
I truly am surprised that Loretta Long (Susan) or Bob McGrath (Bob) didn't remember. (Then again this was 40+ years ago people are entitled to forget small things.)
I guess that with the combination of the test pilots being an intensive process (they would have had to be churned out AND been prepared for scrutiny so that changes could be made left, right and centre) and this being such an infantile stage of the show, it wouldn't have been that hard for him to be forgotten. I've been involved in courses or projects before where people drop out in the early days, and towards the end of them there has been a collective strain to even remember those people.
Interestingly, when Sesame Workshop
first put out the call to identify Saunders, one of the 'clues' was that Caroll Spinney didn't know. This barely seems relevant, since he was not in the test pilots and, it appears, was hired by Jim Henson after they had aired in response to the ned for Muppets on the street. This in itself is a testimony to how information innocently goes astray. Factor in the passage of 40+ years, and you can see how he was lost to the times.