I have seen various posters saying he changed his statements but I haven't examined them as yet. I would imagine his memory is no better or worse than those of his relatives. The difference appears to be that his mistakes are seen as significant but theirs aren't.
I would have thought it quite important to have read the Bamber witness statements prior to reading those of his relatives who are only bit players in the drama while he is the principal. It surprises me that you haven't done that.
I did read as much of what Bamber had to say of any substance, only not bothering with the blog run on his behalf as short acquaintance with it revealed a bit of mind numbing misinformation being shamelessly disseminated from there; and I have certainly built a picture of him from what others have said about him.
I'm not easy with calling witness statements from obviously innocent individuals into question particularly considering the trivia of the substance particularly when considering what Bamber had to say..
I think initially it was a Bamber tactic to attempt to deflect his blame and money grubbing aspirations to the legitimate heirs of Nevill, June, Sheila, and the six year old Daniel and Nicholas's estates after he was found to have ruled himself out of the succession by killing them all.
I don't think it is for us internet detectives to do the work of mass murderer Bamber by interfering in the lives of innocents whose lives have been disrupted enough as a direct result of his despicable rampage.