Darth Venal said:
The line seals it.

Piett was about to clear them even with the older code and after hearing where they were going. There is no hint of suspicion on Piett's part, IMO. To me, the scene almost plays as if Piett goes through this all the time with Vader and is playing along as Vader stares off into the distance for a minute or two. Why is Piett even doing this, since the Executor probably doesn't hang around the DS2 all the time. Shouldn't the DS have its own group to handle this?

The new shuttle design comes from the idea that Vader and Palpatine should have executive shuttles and the Rebels having the same design for "parts and technical" seems rather odd. You'd think they'd have an older shuttle to go with their older code, and for a design we've never seen until this movie (SE notwithstanding), it just makes sense to have an older/different design, at least to me.