Yes - I am fairly sure he said it in interview early on, around or before Shoo Lee's press conference in February.
My assumption is that he hasn't asked for the exact weighting of factors that led Myers / Letby to this decision, and, as you say, that there's no advantage in doing so for him. But there is nothing stopping him from having the conversation with either or both of them should the need arise.
Meanwhile, having seen the evidence from the pre-trial expert witness conference and having presumably read the court transcript, I'm sure he was able to join the dots. But why would he want any official knowledge of it, when he can simply get on and tell the press he doesn't know.
It's all a bit of a red herring, I think.