IMO it is important to remember that this is a Portuguese case first & foremost. Should the PJ have found it necessary to obtain clarification of certain points relating to the Tapas 9 statements then they would have issued rogatory letters to the UK police.
Almost all the original statements taken were done so under witness status. AFAIK it is a criminal offence in Portugal to later alter a witness statement. In the same vein, were the UK police to have re-interviewed the McCanns, neither by request of nor in the presence of PJ officers, those statements & any additional evidence obtained from them would be inadmissible in a Portuguese criminal court.
When SY said the Portuguese legal system is complex, they weren't joking. We have recently witnessed the collapse of the case against Cristovao & his various associates simply because the evidence wasn't collected by the correct authority. No doubt it will be incredibly difficult for the Portuguese prosecutors to get their courts to accept evidence gathered by an overseas authority in the event that same evidence provides grounds for prosecution.
IMO the fact that the PJ do not appear to have ever asked any further questions of the Tapas 9 is further proof they do not consider the group to have been involved in any way.
AIMHO.