jrhone, many thanks for your very informative post.
Consensus here is that if upgrades don't clear in advance, they have to be requested again at the airport, when priority within status is determined by check in time (rather than time of reactivating the request at the airport).
We have also had reports of connecting passengers getting a higher priority on the stand by list. Do you know how that works? Is priority just based on the time you are issued the connecting boarding pass (either at the originating airport or on arrival at the connecting airport)? Or do connecting passengers get a higher priority than passengers originating locally? Does it make a difference if connecting from a domestic or international flight?