I found a couple of references in Marti's Tagbook (pgs. 31 & 126) indicating that for the 1966 model year the warranty data plate that was attached to the door, and the metal strip on the owner card, were one piece that were stamped together and then separated.
The owner card portion was then attached to the owner card and inserted into a clip in the glove box.
Would it be reasonable to assume that this entire procedure, including the attachment of the warranty data plate to the door, took place at the same time - that being when the glove box was present in the car? If that's the case, then the data plate wasn't installed on the car at the beginning of the Trim & Chassis line, but sometime later when the glove box was installed - and probably the underdash wiring harness that feed the emergency flasher and glove box light.