I NEVER get involved in discussions on Trim Tag authenticity because there are enough guys out there that know the facts and can report as such. And, as a matter of fact, Kurt is one of the best, as is Daniel.
That being said, when you first posted a picture of your tag, I knew that it wasn't factory, but didn't say anything. I didn't want to be the bearer of bad news for you, so I chose to leave it alone. I learned long ago that if you can't say something nice, don't say anything at all.
Although I can understand and appreciate your wanting to believe the tag to be correct, due to the fact that you've owned the car for so many years, you have to realize that even in the early 80's, there were people manufacturing reproduction tags for these cars, and reproduction Trim Tags, even today, are fairly easy to spot if you've seen a lot of them over the years. I won't go into details, but there are subtle nuances in the originals that are left off the reproductions.
Fisher Body manufactured hundreds of cars a day and as a general rule, didn't make this kind of mistake. Yes, mistakes were made with Trim Tags, but things like an incorrect paint code, or an incorrect interior code (of which my car has), but not an incorrect date code. You have to understand the process of which these tags were produced to realize why this type of mistake wouldn't happen, and believe me, Kurt knows.
I'm sure no one here will ever be able to pursuade you that your tag is incorrect, just as you won't ever be able to pursuade the guys here at the CRG that it IS correct. But the most important thing is that you enjoy your car no matter what and be willing to listen. Most of the guys associated with this site have 40 years or more of experience with First Generations Camaro's, and have a lot of knowledge to offer. They also value YOUR input as well, so please don't take all this personally. I would hate to see you frustrated to the point where you no longer post.
Keep the lines of communications open with these guys even if it's NOT on the forum!!