Uniform is a uniform is a uniform. It would be a costume if it was a bad attempt to "look" like a uniform, but the BOB ones were not.
From Merriam Webster (italics by me):
Costume: an outfit worn to create the appearance characteristic of a particular period, person, place, or thing <Halloween costumes>
Uniform: dress of a distinctive design or fashion worn by members of a particular group and serving as a means of identification; broadly : distinctive or characteristic clothing
There costumes,get over it.
Unless there relocated "UNIFORMS" from that period of time,which of course they are not.Therefore their costumes.
They're not costumes unless they're an inaccurate portrayal of a uniform. For instance, a child's soldier outfit for halloween qualifies as a costume, as it is simply an alglamation of an idea meant to represent a generic outfit. Meanwhile, the clothing worn in those movies, or by reenactors, are uniforms proper, as they are exacting reproductions of the uniforms. Saying that they are not is like saying that a modern day reproduction of a frock coat suit of the 1880s is not a suit.
I guess it depends on the amount of detail you're looking for though.
You could make a reproduction of a uniform for a movie and have it to be exactly the same as an orginal uniform on the outside yet leave out things that are of no importance in the movie (inside pocket if no dress is ever shown (partially) openend, no inside productionstamp/markings). Any person around you would believe the outfit to be a perfect uniiform, even if they had a very good eye for detail.
One person might call this a costume (it ain't a 100% perfect reproduction), an other might call it a uniform as it comes close enough (all aspects that matter for it's use and looks are perfect copies). =p
Or how about when the outfit is a perfect copy on the outside and inside, only some techniques are different (a slightly different stich, or glueing parts and using fake stiches to make it look like it's all orginal unless you tear the ting apart).
xD
Edit: Personally I'd think I"d go for "costume" when it intended to somewhat represent an outfit (up to 90% match?), "a uniform" if it's a perfect match and "repro costume" if it's near perfect (leaving out minor details no one will ever take notice of for the enviroment/purpose the dress is going to be used for, applying different techinques, whatever) But then you could make a 100% perfect copy that's new, which would also make it... ugh, whatever. I'm spending too much time on this... meh.
