I wonder how the layout of the bar was set in the studio. I think it's quite safe to say that the pool room was not really at the end of the hallway and that it seems to be an entire different set because every time the camera is facing the hallway, we only see a brick wall at the end of the hallway. The one I'm really not sure of is Sam's office. Sometimes I think it's really connected to the bar and sometimes I think it's a completely separate set.

Has any documentary, book, cast interview, etc. ever talked about that?

Trying to answer my own question, I found this page: https://www.pinkish.ro/the-cheers-set/

According to this, Sam's office can be 'merged' with half the set by rotating the other half in place. I can't figure it out. There are "Position 1"/"Position 2" lines but it's unclear what these positions are.

Miniature set designed by Charles Brogdon. THESE are COOL !