Originally Posted by
Bonehead
Relative to the "bucket" that Y-ups come from (if any), note that mileage upgrades (which come from the "F" bucket) may NOT be available on flights that can be Y-upped (I just checked DEN-EWR on 11-7-2008). This suggests that some Y-ups do not come from the "F" bucket. Since Scott indicated that the Gold mentioned in the OP was upgraded via EUA at the 5-day window, he was likely assigned a seat from the "F" bucket, and may well appear on the PDA site's "upgraded" cohort.
Y-Ups come from the A bucket, as noted above. My read of
CO Insider's description of the circumstances is that Mr. 4B was booked on a Y fare but either A was zeroed out or the passenger never called/clicked to move from Y to AU. When the EUA ran it automatically identified Mr. 4B as an elite on a Y fare and immediately upgraded him into AU. While some -Up fares (notably UA and DL) just book directly into F seats, CO's Y-Ups do not as the "up" part is only for elites, so it doesn't happen automatically.