It is true that a person retains 'victim status' until or unless violations of rights are acknowledged and remedied, but this does not, as far as I can see, extend to the court agreeing to adjudicate the existence of a violation relating to any fair trial related matters in the event of an acquittal (except length of proceedings). Indeed, the court states it will not consider such claims and cites the supporting case law. If there are any judgements that contradict this, I'd love to know about them.
The question of what is 'decisive to the outcome of proceedings' is an overarching one. So, whatever disadvantage it was felt might apply at trial as a result of lack of discovery, has in fact not weighed on the final outcome as Amanda has not suffered for it having been acquitted. The court does not want to be swamped by applications from acquitted persons with lingering beefs about the conduct of their proceedings - effectively trying to fight battles when the war has already been won.
The court refers to violations being acknowledged 'expressly' or 'in substance' and to redress. So, if a person is acquitted, it may not necessarily preclude a claim, for example, of a violation under Article 3 for inhuman and degrading treatment, if it is not acknowledged, any adverse consequences eliminated and redress provided. Yet the ECHR encourages States to recognise and remedy their own violations and does not ordinarily set out to punish them after rectifying error.
Having said all that, assuming Amanda and her lawyers make a further application to the ECHR in connection with length of proceedings, there will be an opportunity to argue why the proceedings should be regarded as having been of unreasonable length. Some assistance with this may well be provided in the motivations. Hellmann's motivations, of course, are of considerable assistance in establishing that Amanda's procedural rights were violated - indeed, so were Chiefi's ironically. Across the two applications a lot of ground should be covered by the ECHR in relation to the trial process. Also, Raffaele is likely to apply too.