@Coelacanth18 I think you and I are in the same boat! Fortunately, most of us live where there are only Common Goldeneyes, so we don't have to work too hard on the identification. I've only seen Barrow's Goldeneyes twice - at Grand Tetons in 2019 and Yellowstone in 2023, so I'm certainly not an expert either!
@birdsandbats I have tremendous respect for your birding knowledge and you've been correct more often than just about anyone else on this forum! You and I are in the same situation when it comes to these goldeneyes - we see a lot more Common Goldeneyes than we do Barrow's Goldeneyes and this is a tough pairing of bird species to tell apart. My default is Common Goldeneye and the only reason that I looked at these closely is because I struggled with the identification of Barrow's Goldeneyes at Yellowstone NP last summer and it's fresh on my mind. Thank you for your careful examination of this flock and for helping so many people on ZooChat with their bird questions!