I'm more inclined to think that they have interviewed around 120+ in the past week for 100+ jobs. Within that they will find that some are not suitable, some currently employed who went to Leeds to see if "the grass was greener on the other side" and some not willing to accept their T&C's despite being fully briefed before going attending.
When you combine that with a start in about 4 months they surely know that a number they select will be snapped up in the intervening few months by a host of other airlines who seem to be growing their pilot workforce then an extra advert seems to make sense.
They may also have a higher attrition rate than projected over the winter from current employees.