If you need a deeper building, it's easy to make new sides, especially for mid-block buildings. Depending on the height of the neighboring buildings, plain styrene sheet can be used, or brick/concrete block textured. It doesn't have to match the "fancy brick" on the front.
Also, all buildings in a block aren't necessarily the same depth. Some go all the way to the alley, others have parking behind them, or space for delivery wagons/trucks.
Then there are the corner buildings, like the one I found years ago in Heppner, OR. It had fancy cut and polished stone blocks for the front, on the main street. The long wall on the side street was rocks. Not even cut stone - ROCKS. It looked like they had built forms, poured them full of random rocks, grapefruit to basketball sized, then poured mortar over the whole thing. By the 1980s much of the mortar had eroded away, leaving all of these round rocks half-embedded in the wall. It did have a few side windows, on the second floor, just holes cast in the walls with wooden windows, recessed a foot or more into the wall.
Many old brick buildings had thick walls. Many of today's are frame construction with a brick facade. Back then they were always at least two layers of brick, sometimes three, and could be a foot or more thick. That's what the "header" bricks, individual or entire rows, are for - they tie the layers together.