LNIDA, the shortage this year (which I've heard has now been plugged) is in no way a result of the recruitment process itself. All roles were filled back in the autumn using the silly HR tests.
The miscalculation was that out of work, type rated pilots, with families to feed were not going to take the first solid offer that came along. Baby pilots should have filled all the vacancies, but they got solid offers from FlyDubai, Norwegian, Qatar, Ryanair, Monarch etc with start dates prior to the dates Jet2 "promised". So unsurprisingly they went elsewhere.
Nothing will change next year because we are now fully crewed. "What's the problem??" will be what HR will say. They've even saved the company half a years wages from 70 odd pilots, so will probably get a bonus!