Problem with your theory is that the shadow of the Shuttle is on the big head NASA guy’s face... and there are no stars in the shots.
IOW, it’s a model. Shot on a set; here it is again:
NASA: HOW TO FAKE SPACE BADLY in 1983
https://www.youtube.com/watch?v=h9i8tMzxIn0
And as someone who’s edited old time video formats, not sure what you are referring to that this is a dupe error with projectors? Are you saying they would have used a kinescope set up for tape to tape?
That would be ridiculous. Just make a dupe.
The contours of the blanked out area do not match the silhouette of the shuttle. If anything, and this theory were correct, it would be a part of the structure int he back of the model holding it up. But if I were making a model with open area behind it for replicating outerspace at near earth orbit, I wouldn’t have dark structure in the shot. So it’s probalby not even that. But it’s definitely not shadow.