DutchC,
Pilot recruitment is really hard to predict. You can use historical data to measure the attrition rate due to lost medicals, people jumping ship to other carriers etc but it's only a best guess. Also, delays to aircraft plus launching new routes (say an extra day downroute) etc also impacts pilot requirements. They can't even predict how many FPPs they'll need next year nevermind in a few years time. I think the figures banded about were just best guesses and probably erring on the conservative side. If the FPP is a success (the first intake is flying the line already and it appears it is), then it wouldn't surprise me to see BA extend it. Nothing in aviation is guaranteed so if you can, apply when it next opens.
I completely understand your dilemma though DutchC. I didn't apply for FPP 2011 because I'd just finished uni and was actually in the process of joining BA on their graduate scheme. I was already under enough pressure as it was with assessment days, referencing and finding a place to live so waited until 2012 opened.