Not necessarily SiL. When you have a large group of people talking amongst themselves - what one person may have missed - another one may have noticed.
For instance - IIRC at first Russell thought Jayne had left the table at the same time as Gerry. However, on discussing it - Jayne would be able to remind him that she left after Gerry because she was still there when they began wondering where he'd got to. (watching football was suggested as the reason).
As soon as they had finished writing down the timelines - they handed it to a policeman who was with them. Apparently he said ' thats what we want' - so it could be they were asked to write it down. (from memory so could be wrong).
I'm sorry. I don't see Jayne 'correcting' Russell before first interviews as the way to go. It was the job of the PJ to detect and sort out any conflicts, not the T9.
I'd have the same issue if any other cohesive group got together and sorted out what they were going to say, in advance of interviews. I seem to remember at least one dog team did that, and produced statements that are worded nearly identically. Is that how it is supposed to work? Not for me.
And some of the very odd times we've got from staff. Should those staff members have got together in advance to work out the collective tale? Again, not for me.
I got assaulted once (very minor). The first thing the police did was to separate me from my partner so they got independent statements from both of us.