The website says, as quoted by WineCountryUA: "As customers check in, they will be placed on an airport upgrade standby list. This standby list will clear after check-in is closed, and is based on Premier status and fare class. "

It says "based on Premier status and fare class", but it doesn't say HOW it's based on Premier status and fare class. It doesn't say "ordered by premier status, and then fare class within each status".

It is absolutely possible to use this subset of the "5 day list" priority (removing GPU/RPU/Miles+Cash) and still be "based on Premier status and fare class":

Premier members on eligible Y- and B-class fares, as well as Premier 1K members on M-class fares, sorted by fare class, then Premier status
All remaining Premier members Sorted by Premier status, then fare class and award travel

So, this is valid: Y GS, Y 1K, Y Plat, Y Gold, Y Silver, B GS, B 1K, B Plat, B Gold, B Silver, M GS, M 1K, remaining GS sorted by fare class, remaining 1K sorted by fare class, ...