Originally Posted by
PMMMDL
Rule of thumb:
Never purchase an M+ fare for upgrading unless there is Z availability at the time of purchase.
Especially for TATL legs, there should be Z availability on a flight from at least one gateway.
I agree completely. I do TATL monthly (MSP -> Sweden) - and the only time I will pay the 30+% "surcharge" for the M fare is when the upgrade is available. I have had pretty good success using SWU's this way - but have had to be flexible on the flights (sometimes going via CDG vs. AMS or doing MSP->ATL->AMS or MSP->DTW->AMS).
Not sure if this will help the OP or not. Only tried once to use the SWU "same-day" at the gate (was a flight AMS->MSP) and the KLM agents told me in AMS that it wasn't possible (based on their ticketing system)