Originally Posted by
CO EWR CPH
But isn't there a distinct disadvantage to being absent from the EUA list and relying solely on the "battlefield" (ugh, I hate that term) upgrade? This same thing happens to me when the first flight is on UA and I am connecting to CO - you can't check in on CO - you won't even get the option to do so. I always do check in with UA first, but that doesn't seem to trigger anything perceptible in terms of your place in the upgrade queue.
You have it backwards. When you check in with UA and your second flight is on CO, you are still on the EUA list (you are always on the EUA list when your CO Elite FF# is in the reservation). Checking in with another airline only prevents you from being on the Battlefield Upgrade List. This can be corrected by seeing a gate agent and having her manually adding you to the list.