PLYNCH - One thing we have to ask ourselves about this idea concerning the so-called 'stolen technology' is that - at least by my thinking - it might NOT be based on the Constitution Class Starship design, as we know by the ENTERPRISE we see on the screen at the time of the episode.
From what I am thinking:
1. SPOCK states no Romulan or Human has had any contact since they fought with sub-light ships 100 years prior,... therefore, does that not presuppose that if any 'technology' was stolen, it would be based on the old-style sub-light vessels - and not a current Starship of this size and hyper-drive technology,... and remember, SCOTT states the BOP is "simple impulse power',... and yet, we see what appears to be, by assumption, warp drive nacells,...?
2. If I recall, is there not a line of dialog which states,... a 'small' ship,... when describing the BOP?
3. Even if they had 'stolen' a Starship, and even if those old sub-light speed ships were the size same as the ENTERPRISE hull design, why do we assume they didn't change what they had to suit themselves?
4. Because the dialog expresses an idea apparently 'based on design', so does that absolutely mean 'made out of',... ??? they (Romulans) might have used zero physical material from the captured sample, and created the BOP based on 'conceptual design elements' only, and does not automatically mean a 'retro-fit' of an actual old SFC ship.
,... or does it?