“As you have noted, the colors of the patch and shoulder straps and the rank are wrong for Scotty. My guess is that they took a shirt that already existed but not needed for Scotty and used it for another cast member to avoid having to create it anew. It might have seen the screen but not on Doohan.
One thing that I noticed is that the material for the shoulder straps has often faded over the years for some of the divisional colors. Check the pictures in your Christie’s catalog for the security (gray) and medical (green) straps. They are almost tan now. But other colors such as red and orange have fared well.
Incidentally Spike’s great ST uniform site has this very image of the shoulder strap featured and explains it as belonging to a crewman second class.”
And from another buddy:
“Another case of a costume made for the movie and not used. We have seen many of these so far, (Rand last week, McCoy in the upcoming Profiles auction). I’m sure this one is a relisting from the week 2 or 3.”