There is no excuse for the polar claims made in these documents prepared by the Bamber and those supporting him. None whatsoever!
Your 'polar claims' thing sounds like it was taken from Vic (family spokesperson) on the road to Damascus. Where he goes from being sceptical (or at least open minded) to believing in Bamber's guilt, as if he was Ann Eaton her self. He used the same reasoning.
People who believe Bamber is guilty wont consider the shock / disorientation argument in an innocent scenario (as they quite obviously assume a guilty Bamber would be alert, aware, controlled, prepared etc.)
What about 1980's police interviewing? Stan Jones is at him. Over and over and over and over and over again. Trying to get Jeremy's back up. Trying to be cocky and unpleasant towards him. Trying to needle him. trying to get him off balance. Trying to unsettle him. Not in a clever way but in a harassing manner.
What did the police say to him about the calls? What did they try and plant in his mind? 'We know you did this' 'we know you did that' etc.
And what was the catalyst for Bamber changing his timings anyway? If it was the release of some kind of police document, then how can you blame him? My mind plays tricks on me all the time. If a child or anybody provides a completely contradictory version of something to the one I recall myself, eventually, I start questioning my own version.