Dan! In general I think you definitely right. Re the trunk lids all 65 Dart GTs I have owned over the years (9 cars) all of them had the black tejp under the trunk moulding. Those cars were assembled both in Los Angeles as well as Hamtramck.
Re the assembly staff I think they had one model for Dart, one for Dart 270 and one for GT. But if those was out of stock they took a trunk that was spare part. That's the reason for holes just for the centered letters! That could not be applayed to the assembly line work. That would be too time consuming!