This particular question has been done to death. However the question is worded, the answer remains, how is it possible to talk about, let alone prove, something which never occurred, therefore, why would it have been necessary for Bonnett to make such a statement?
No, that's not even the question. Here you show your own bias. Think about this logically. We have a situation where Bamber has just killed five people, in cold blood, but is considered in the clear because he's saying that he got a call from Nevill. The police had rushed to the scene, in the middle-of-the-night, to find that Sheila had shot everybody and then killed herself. Surely this Bonnett fellow would immediately be shouting and screaming:
"But I was the operator who dealt with the incident!! I compiled the incident log! I recorded only one call and managed the incident. There was no call from Nevill. Had there been, I would definitely know about it."
And that, I'm afraid, is the truth - had there been a call from Nevill, Bonnett must either have taken it himself (which explains why he later spoke to West), OR he will have been alerted to such a call.
It follows from this that your
negativa position about the logic chain could only work in the absence of evidence of a call from Nevill.
And....oh dear....there
is such evidence. That's a bit of a b.ugger, isn't it? The crux of it is that there is no reasonable explanation for why Bonnett and West recorded these calls as they did and for why Bonnett did not contradict the police.
This of course explains why you are so keen to dismiss the idea that the documents record two callers. If they do, then the whole case collapses - which is very embarrassing, to the say the least. Not that I'm saying Bamber is innocent. Please understand - and I need to make this clear - I hold no brief for Jeremy Bamber. I'm not suggesting he is in any way innocent.
Just to take this discussion further, I've given you two reasons (which I will repeat below) that would cause me to change my mind about this. If you can show that Bonnett wasn't taking (or being passed) calls from the public or that Bonnett in fact did alert the police that they had got it wrong, then the whole situation would resolve itself and it then becomes a question of: Do we believe Bamber or not? Is Bamber just unlucky? Etc., etc. And then it's conspiracy theory time and alien lizards.
We are, here, at the very crucible of the Crown's case theory. This is why Julie Mugford came into the picture, despite the fact she had nothing probative to say and was in no way a reliable witness. The police needed somebody to add a bit of 'tinsel' to a very weak case, something that would reinforce Bamber's criminal motives.