Yes, there are historical examples of taller rowhouses that can be referenced by people doing additions

This is a three story frame rowhouse on Capitol Hill.


This is a building that had been two stories, and has had a third story added.  The windows are undersized and lack stronger features surrounding the windows--framing, lintels on the bottom and window hoods on top, and the cornice needs to be more prominent.

I can't remember exactly where it is, it's around 13th and Delafield Streets NW.

While this diagram is of a commercial building, many of the architectural features of historic commercial buildings are shared by historic residential buildings, at least when it comes to windows and cornices.