I thought the trim was part of the premium level and I thought being a GT put it in the premium level, mine 67 Dart GT convertible has the trim, and the fender mount turn indicators. Was going to say that it is possible that some have swapped parts from a 270 hardtop, but I think the 270s had the trim also(my 67 270 4 door did, anyway). Just guessing but I would say that some have filled the holes to avoid looking for better trim, I would guess(haven't looked yet)that the trim is hard to find being a 67 only item.
Guess, I wasn't much help, but it is nice to meet another 67 GT convertible owner.