Bingowings said:it's never made 100% clear and it doesn't need to be.
That's how I feel about this whole thing. Vader is leading Luke on a long, creepy wild goose chase through a building we know little about. That's about it. I'm all for fixing continuity errors, but not everything has to be explained ad nauseum.
Besides, any technical stuff we read about is usually written after the movies are done and often altered several times over the years, so...?