I've been looking through the availability of SeatFrog upgrades on CrossCountry services. The hourly departures from Edinburgh (at the :04 or :05) consistently have upgrades available, except for the daily 0820 Aberdeen - Plymouth, or the 13:05 Edinburgh to Plymouth/Cardiff, when there are upgrades only available on the occasional day (regardless of how far in advance you look). Does anyone know of a good reason why this might be the case?
(I'd even thought about swapping my train so that I could upgrade, given that the upgrade on almost all journeys appears never to go much above the minimum allowable bid, but availability of train-swap on the XC services also seems to be pretty non-existent)