First: Marketing was intended only to sell tickets, not to provide insight into Lucas’s artistic vision. It’s irrelevant to this discussion of Lucas’s intended viewing order. Why did you bring it up?

Second: OK, I believe you. I was going by IMDB, which may be mistaken. Where is it on the DVD? Not that the presence or absence of “is” is material to the discussion. Before ROTS was released, the Saga had not been completed. With the release of ROTS, the Saga was complete. That has nothing to do with Lucas’s intended viewing order.

Third: Lucas can release the 3D versions of the films however he darn well pleases. The fact that he has chosen to do so in 1-2-3-4-5-6 order is a pretty strong signal that he believes the films are best watched in that order. He has stated the same in interviews. Now it’s possible that his views on the subject have changed over time and that ROTS was intended as a conclusion when he made it, but absent evidence of such a change of opinion, there is no evidence that ROTS was intended as a conclusion. ROTJ clearly was.

Not that Lucas’s intent is the end-all-be-all of the discussion. Ultimately, what matters is what works dramatically. IMO, ROTJ makes a much more satisfying conclusion to the series than ROTS does.