Surf Scoter follow-up

I returned to Brush Hollow but the Surf Scoter was not present which is unfortunate as I wanted to check somethings to help in determining the sex and age of the scoter. I don't have a lot of experience with scoters and had only Sibley's

Though the scoter slept/rested with its head tucked for most of the 15 or so minutes I watched it, I could clearly see a white patch below and behind eyes though no visible white in loral area. The top of head was darker giving it a dark cap effect of Surf Scoter instead of White-winged-plus no white on wings.

I am not sure if this was an adult female or a bird in Basic I plumage since Birds of North America states, "By late fall (Basic I plumage), coloration of immatures begins to differentiate by sex: Male assumes blackish cast on head, neck, upperparts, upper breast, flanks, and undertail, these areas sometimes becoming wholly black later during winter" And "Thus some birds are making transition from Basic I to Alternate I in Nov, while others do not make this transition until weeks later" If I read this correctly, immature Surf Scoters should be in Basin I with some already transitioning to
Alternate I by now.

SeEtta