"Would you buy a used starship from this man?"
There will always be factors that lead to new designs being considered, solicited, and built. As noted above, both common versions of the Type T plans have "issues". If we assume that "issues" exist even in the real thing for some subset of the potential customer base, then variants will appear.
Case in point, and one that seems to have snow-balled, is the Type A2. While reworking the A2 (by restatting to 400 tons to match the plans) for my campaign, it was noted by my players that there was "no way they were going to traverse an airlock in their PJs to get coffee in the middle of night-shift". Thus was born the corridor between the two halves of the crew quarters, to provide a buffer against the fore cargo lock and the cargo bay. In due course the deckplans were finished and posted to my website, and now that corridor is popping up in other renditions of the A2 all over the web...