During the first season of Star Trek: Discovery, we had a chance to see a schematical view of a Constitution-class vessel USS Defiant, and later "space view" of the USS Enterprise, a starship of the same class.
Is there an in-universe explanation for the differences between the ships? They should both be from the same time, of the same class, and yet the differences are significant. The Defiant looks like it could look like this in the mirror universe, however, in the episode "Despite Yourself", which does take place in the mirror universe, there is this dialogue, which suggests that the Defiant is indeed from "our" universe:
Lorca: Data from rebel intelligence suggests that we're not the first ship from our universe to find ourselves here. It cites another Starfleet vessel: USS Defiant.
Burnham: It's unclear, but data suggests that in the future, Defiant will encounter a phenomenon that'll bring it into this alternative universe's past.