Well, they might have had more than one, of course.
I just looked up feek61
's excellent research
on the issue and that tells me that the red GNDN panel ("WP5") was a permanent
part of the large panel with the horizontal alert indicator / speaker, accurately reproduced
by Donny (post # 87).
Apparently they only
removed the large panel in "Is There in Truth No Beauty?" (no A-frame corridors this episode) and attached it in the main corridor
to simulate two different corridors during the ship wide call.
It stands to reason we are looking at a unique piece of production decoration where either you remove the whole panel or leave it be. Therefore, it's probably just the plain red panel in the exam room in "Let That Be...".