Thanks for giving birth to us, Mater! (Sort of.) 
I think CH is absolutely correct in that GA and JI are likely to be constrained by their contracts from saying anything damaging to the film.
Interesting that she said that during the period the Walkers were supposed to be homeless they spent six months living in SW's deceased mother's cottage (which, added to the eighteen months they spent at SW's niece's flat, must give them a roof over their heads pretty much throughout the period of 'homelessness'?)
Also of interest that CH said that for all the Walkers' claims that they have always used the names Raynor and Moth interchangeably with Sally and Tim, everyone she spoke to who'd known them for some time said they invariably addressed one another as Sal and Tim, even though some people who'd met them more recently said they introduced themselves initially as Ray and Moth.
And that all legal documents, bank accounts etc used Sally and Tim Walker. And that SW had been very cagey about telling early interviewers what 'Moth''s real name was.
(I laughed at 'Moth is just Moth, like Prince or Madonna!'
)
The other thing I noted was CH saying (in response to a question about whether supporters and friends of the Walkers had also emerged during her investigation) that absolutely, they had their supporters and were regarded as nice people by some (she mentioned the neighbours who knew them when they lived in SW's mother's cottage as thinking they were 'lovely'), but that those people had tended to respond with hostility to her approaches ('I know who you are!') and refuse to speak further.
And that, in response to a question about why any of this hadn't emerged much sooner, CH reiterated that many of the people involved/injured were 'unworldly' -- that the surviving Hemmings family members and former employees of the family firm had thought they were possibly also constrained by Martin Hemmings' NDA, that SW's niece who handed over the confession letters at a service station had spent much of her life living on farms, didn't 'come up to the city' a lot, and was very nervous about talking to a London journalist.
That someone (possibly again the niece, Anne?) had tried to contact PRH twice, but just got through to a switchboard and didn't seem to have managed to speak to anyone in any way that was useful.