Yes they are. Sets are window dressing. Costumes too.
And I hate it when productions take this view with historical events just as much as I hate it mean studios decide they don't need to keep anything the same even if they are using the exact same place and time within their own fictional universe. It is a "you already know what it looks like and have plans for the sets, why design a new set for something that shouldn't look any different from the last time it was seen within the franchise? Especially when it should still look like that the next time, in continuity, it is seen again. Even those that was 10 to 50 years ago TV time." (At this point Doctor Who gets invoked and the old TARDIS sets and episode costumes are recreated for appearances of the First Doctor era during the time of the Twelfth Doctor. I mean, if the BBC can do it, CBS should certainly have the funds for it.)
Of course this is also why I am not in theater, or any of those productions...I was trained as a historian. Things not being accurate to history both me sometimes. While I can understand it with productions that can't used real tanks or the location shooting can't be accurate because they built a track of houses over the old battlefield, for a fictional setting like Star Trek, where the studio can control the sets from day one...it shouldn't be that hard to recreate a place that was a set to begin with. Especially if the intend of the episode is to reflect that location. A studio shouldn't just come up with a story to be set on the USS Enterprise for an episode or two, and then make the ship look completely different from what it was before. What would the point be of using that in the story but making it totally different in a time period, within the show's continuity, where it should look like it once did back in the 1960s? You would think that the nostalgia angle would be part of the story's makeup to begin with if they plan to drag the Enterprise into things.