I think the one and only time (but I'd have to think about it more) we saw benches on the set officially labeled as "INT. BRIEFING ROOM" was in "Turnabout Intruder" when Mister Spock was being tried. I think any other time we saw benches in that room, it wasn't actually the "INT. BRIEFING ROOM;" it was redressed into something other than the Briefing Room ("INT. CHAPEL" or "INT RECREATION ROOM," for example.)
Similarly, the flags were located on the "INT. HEARING ROOM" set (which, of course, looks remarkably similar to the Briefing Room). I, too, would make the Hearing Room a separate build-up.