Mike, I can't say for sure when these entered production, but if you look in your 1967 AIM (UPC N10, Sheet A4), there's note 8 that states "ITEMS 13 & 14 ADDED" and the date is 11-25-66.
Of course, that's not the date the change went into production, only the date engineering submitted the information to the art department, so who knows when it actually started.
However, your Coupe should probably have the rivnuts. Yes, I suppose they can come out, but because they're designed like a rivet, when the screw/bolt is torqued down, the rivnut expands in the hole and it would be hard for it to "just fall out". And you should only have the tapping plate on the passenger side of the car. If you have tapped holes on the driver side of the car, then I have no explanation because the rivnut was inserted into a "drilled hole", not a "tapped hole".
Can you post a picture?
Ed