That's not how the movie industry works, everything is built quick and dirty and any masters are thrown away to make room for new models for the next episode. Rel has recreated the Defiant for his master model pretty much the way the original model was created, no molds were made of the finished Defiant model, no reason to, they only needed one for filming. The truth is Rel's Defiant is way more finished and refined and better built than the original model.
Brave little ship !!!