It seems I was wrong: GA weren’t ignoring me as I’ve just received a reply. Unfortunately it doesn’t say anything more than previously.
GA: It’s valid everywhere in z1-9.
TfL: It’s valid everywhere in z1-6 and some [unspecified] places in z7-9.
GA: If it doesn’t work the gates that’s TfL’s problem [true, but unhelpful].
TfL: It doesn’t work the gates at stations where it’s not valid.
The one thing I asked GA to do – discuss and resolve the issue with TfL rather than leave the customer stuck in the middle – they clearly haven’t done and have no intention of doing.
This is what happens when you have a fragmented railway and local control. None of the companies care because they can each blame the other, to the detriment of the customer.
I confess to being bored now: I’m happy with the z1-6 element, and I’ll use Oyster for the rest.