Celtic Mech, thank you for your very clear explanation
Coming a little late, and about the Nav ADR disagree message, the BEA (French investigation preliminary report) explains it thus:
Signification : ce message indique que les EFCS ont rejeté une ADR, puis
identifié une incohérence entre les deux ADR restantes sur l’un des paramètres
surveillés.
That is: this message tells that the EFCS have rejected one ADR, then has identified a discrepancy between the two remaining ADRs concerning one of the parameters.
For what it is worth...but as they work closely with Airbus I think we can trust them on that.