You will be in with a good chance just like anyone else if you apply before the deadline so don't delay.
But once that date had passed and invites were sent out, the people who hadn't been invited for assessments were put on hold until the invites to the group stages had gone out and the spaces were full. If there were not enough people making the standard for the group stages or people didn't sign up for a day in time then they would invite other along for the online assessments and see if they can then fill the spaces in the group stages.
This is all from what I had seen progressing through the various stages to the final interview. Aer Lingus did not say this is how they work, just my take on it - once spaces for the next round were fill, PFOs were sent out to the people still waiting.