perhaps, but up until a couple of hours ago a few thought that was the case for the APC. I wouldn't discount anything unless there is hard concrete tangible evidence to say otherwise.
Star Wars is a good example of this, it's been assumed that all known packaging variations etc have been well long documented, but last year a European Jedi version of the Darth Vader TIE Fighter surfaced, something never seen before, but done in such low, low quantities that it was assumed there were no variations. I'm also aware of another biggie, but the news hasn't broken yet, but the Star Wars community will go nuts when it does.
In the absense of no-one having one in their collection so far, does not mean they couldn't possibly be out there. Equally there may be collectors who have one, but just oblivious of the signifficance.
No-one may have thought there was any unproduced material out there, and then out of nowhere, Boffin popped up.
You never know what may surface, but as understanding and knowledge grows, so will the possible number of confirmed sightings.