Im guessing things could possibly roll over into next winter if there are enough internal upgrades passing the mark.
If they didnt have enough Capts with the upgraders then Im sure they would have notified the external candidates by now for the summer season.There must be many more in the hold pool than they need.
Time is running out as last courses are probably April for this season, so perhaps 2 mths left to hand in the 3mths notice.
How long does the hold pool validity last before having to start again?