According o the BBC passengers whose flights were cancelled with the IT debacle are entitled to a full refund or a rerouting before November 2017.
Of course Regulation 261 provides
(c) re-routing, under comparable transport conditions, to their final destination at a later date at the passenger's convenience, subject to availability of seats.
There is no mention in the regulation of a re-route before date. The regulation intentionally doesn't mention a specific period as
passenger's convenience will differ from person to person.
Repeat a lie often enough and it becomes perceived as the truth.