What .Mac said.

The logic with having some shuttles in the background is

A.) Working on a large battle station, there needs to be some “traffic,” secret building or not. The station needs supplies and building material.
B.) The heroe’s course catches the attention of the Executor since it is going to the planet and not the station. That is why it seems “out of no where” a shuttle is appearing and going to the planet and not the station since that’s what is being worked on.

No dialogue needs to be altered and doesn’t mess around with Vader sensing or not. Even if the viewer does not know what happens in the movie next … when watching the original, it seems pretty clear the “sensing” appears after Vader’s question and begins “pondering” about it. (scene with Vader looking away) Sorry if I am not quite understanding your thinking Jan-wan.

Granted, there does not need to be thousands of shuttles (or enough to litter the scene of vessels) since the emperor is not having “all hands on deck” to build DSII since he wants to cement the idea of the Rebels that the base is incomplete and is “vulnerable.”