tnk479 I am not at all an authority on decoding Google Pixel packaging.
My personal history is one 3a ordered from Amazon (unlocked easily), one 6a ordered from Amazon (could not unlock, thus returned), and one 6a ordered from Google (unlocked easily). Both of the 6a's had the same SKU (GA03715-US). The early 6a's were unusually hard to unlock. I think I correctly went through all of the recommended rituals to unlock the 6a I got from Amazon, but who knows?
What I do know is that Google's end-user support flatly refused to provide input on unlocking a device purchased from anywhere but the Google store, and that 100% of the purchases I have made from the Google store (i.e., one purchase out of one purchase) unlocked easily. Meanwhile, there are many reports of people buying "unlocked" devices from Best Buy and easily unlocking them.