I have also found areas that are see through. There is no texture, no black are, and you can just see into the next room.
Would this be from the model being unfinished as well?
Yes, depending on how you define "Unfinished". Most of Bioware interiors had no ceilings etc. By Design. So, technically they are not "unfinished", but are just "not what you wanted" types of things. However, in a set that really does have most ceilings etc, then yeah, I would consider a few without ceilings as being unfinished.
If they have the "black texture" assigned, that was definitely by the choice of the model maker for that particular tile, or was placed there as a place-holder until they got around to actually mapping the correct texture into place. Remember, sometimes you have to adjust the mapping of a texture on a given object as the defaults just won't line up correctly etc. Especially in the pics you have shown, those ceilings are very detailed AND they have long lines running the length of the ceiling that must be adjusted to correctly line up to the next tile or object that has a texture applied.
Basically, it looks like you found the tiles that were added in an in-complete state or were copied from other sets that never had ceilings, depending on which tiles you are talking about.