I don't understand why you've bought their story about 'new rules'. This is nothing to do with 'rules', they don't have enough pilots. Period. They don't know which flights are going to be cancelled, because they don't know who is going to call sick, who is going to go out of hours because of a delay, who is, god forbid, going to call fatigued, who is going to fail their command check.
Simple fact is, they have nobody on standby. Anybody on standby is only there because they don't have enough hours to be of any use during their five days on. So no, don't expect them to identify their October cancellations in the next few days, and don't expect them to Wet lease aircraft that will sit idle in Stansted whilst a flight from Bari is cancelled.