There seems to be a time period from Oct 17th to Nov 21st where activity did not count towards your new AC tier, but where you will not get tier credits for it either.
I've been in touch with AC via the Aer Lingus twitter a/c (a very unsatisfactory way to communicate with them) and it has been confirmed that all my activity since I moved to Prestige (July 2016) is being wiped from the record. So someone who was Prestige in July 2016 and ceased flying for the rest of the year is being rewarded in same way as someone who flew 7 TATL flights return since then. It's strange logic to me but when I look at how the whole AC things has been rolled out ... I suppose it fits.
Ce la vie. I'd love to be able to say I'm taking my business elsewhere but the reality is that for services to ORD, there's very little option save routing through LHR. So I'll still be spending my money with Aer Lingus but I'll be doing it a lot more begrudgingly than I did in the past.