I am far, and I do mean far, from being the "camaro expert" that many of the posters on this site are, and I mean that respectfully. Myself, I have been on this site for years and have just starting posting about a year ago but I don't feel the need to chime in at every moment, like some others that like to hear themselves type! lol
That being said, I try to gather information from people who are "so-called experts" i.e. Jerry MacNeish. Although he is probably regarded as more of a Z expert rather that an SS expert, his book does address this topic. For the record, he states that the aforementioned panel is "satin black" color. Based on this information, and many, many other cars that I have personally seen at shows, etc. I had my tail panel re-painted satin black, from the gloss black that it was when I found it. Even the guy I bought it from stated that it was wrong (he wasn't an expert either).
Anyway, right, wrong or indifferent, we can only base this color on published information from reliable sources or better yet, true survivor cars that are still out there. I would bet that there are more cars with the satin, or 60% gloss than there are the full gloss panel. Is that correct or incorrect. It's like the old tootsie-pop commercial with the owl licking the pop, he says "the world may never know".