Yes, we could argue that there was certain writer intent in "BoT" that later got contradicted, regarding the size of the RSE. But "BoT" already seems to contain a contradiction of such intent in itself...
Isolated behind the NZ for a full century, the Commander and the Centurion still manage to have a shared history of glorious battles. A century previously, a Vulcanoid man looking exactly like the Commander here hadn't even been born! So the suggestion is there that the NZ-constrained volume actually contains enough star systems for military campaigns - and we can argue that one isn't "enough", because the Commander is an apparent veteran of starship
On the other hand, we need not assume that the area hemmed in by the RNZ contains anything else besides the Romulan Star Empire. Starting with this episode already, we learn that Romulans are psychologically perfectly capable of having wars with themselves!