After reading this thread I still do not understand why Eurocontrol is going to charge Ryanair the MTOW of 74990 kg.
What I understand from the Eurocontrol FAQ is:
"The MTOW declared should be the maximum certificated take-off weight of the aircraft. In the case of multiple certificated take-off weights, the MTOW to be declared must be the highest weight
authorised by the State of registration."
It does not say 'authorised by the aircraft manufacturer'
Each and every Ryanair aircraft is registered at 66900 kg in the Irish aviation register. And that is what Ryanair reports to Eurocontrol.
Latest Register and Monthly Changes - Irish Aviation Authority
However they use higher MTOW on some flights but that is okay if still under the MTOW specified by Boeing.
Is this some trick by Ryanair to have a lower MTOW registered?