Ok, although there's no definitive answer here as of yet, there's something about GMSPO that needs to be said. Although I've never been an official parts jockey, I've got over 40 years of buying OTC GM parts and working closely with the GM parts guys, and even having my own setup to look up GM part numbers when my old parts guy was still alive. He gave me his creds (when he shouldn't have) to keep me from bothering him too much.
Could even order parts via SPAC if it wasn't in local warehouses. PITA, but it helped a few times.
GM does not service every part on a vehicle. Some are considered "standard" parts like fasteners, corrugated wire looms, etc. Some are specific parts. And SOME parts are part of an assembly. Some are even labeled "NS", aka, not serviced. They may have part numbers cast or stamped on the individual assembly parts, but that's just used in engineering and the parts vendor to put together the right assembly. The parts aren't necessarily available separately. One example of this is plastic brake master cylinder reservoirs that come with new rubber seals to the master cylinder itself. BUT- the seals are NOT available separately. Buy the resi and you get the seals. That's the only way you can purchase the seals.
This is what I believe is the case with this secondary trunk seal. My seal too looks like Parts Peddler's. Here's a pic of the 2010 I took just a bit ago. Ew, I gotta clean out that gutter. WTF.
