If they were going around future demand, they could have just staggered start dates out a bit or put people in a hold pool. In my current role (non-aviation), I sat in a hold pool before being assessed, then entered the "successful" pool and after a few months was given a start date, the entire process from start to finish took about 15 months.
Easyjet are a huge airline and therefore having being a few pilots over or under their requirements shouldn't really hurt them. The only way I could understand them going back on an offer due to a problem at their end is if they were in serious financial trouble or similar.