You are probably correct. PPG may very well be the supplier and mfg. the OEM glass. The fact is that logo, be it BMW or GM, adds hundreds to the cost of the glass, and it's what came with the car. Again, from experience in the BMW world, with the logo is OEM, without the logo is "premium aftermarket." Safeco is aftermarket. The thing I'm trying to stress is that in the pecking order, the glass with the logo on it is OEM, costs the most, and is what came with the car. The one without the logo is not OEM, it isn't what came with the car, it costs less, and it can even be made by the supplier who makes the OEM. But it isn't OEM, it's either "premium" aftermarket, or aftermarket. It is not identical as some would like to claim. The installer wants to make the most profit he can, and that's not happening on the one with the GM logo. He can't just get it anywhere, he has to get it from someone who is marking it up. That's his motivation from steering you away from it, or if he can, tell you that it doesn't exist.
Why would Safeco want to sell you aftermarket, netting the lowest price, when compared with OEM? They work with insurance cos. (you schedule right from the insurance cos. web portal), and they have the highest margin on safeco glass. When they install OEM, they may colllect $750 from you, but the mfg. and distributor pocket the profits, not safeco. They would rather you pay them $230 for their glass.
But when you pay $0, or $100 deductible, what glass do you want? The one that costs $700+ out-of-pocket, or the one that costs $230 out-of-pocket?
These shenanigans go on all day long with auto parts, can you buy a "new" brake caliper, or a "new" alternator, or "new" a/c compressor? Insurance cos. and people who contract with them will tell you no, aftermarket is just as good.
When it's time for a new windshield, I'll try my best to get the GM logo (insurance may resist, I dunno, I have that hands co. now not the lizard). If I have to settle for PPG which is what I think is premium aftermarket, maybe that's the reality. But when aftermarket didn't fit, the lizard co. paid for the BMW OEM with logo on my 335. Maybe it'll be the same with the Enclave....