Jury should have been told.
The jury is told what the prosecution and defense choose to tell them.
None of us decide that.
Anyway the newly fitted catch is irrelevant, regardless of whether the defense knew about it or not.
The method used to get into the house does not affect the outcome of the case, as described in the CoA notes 2002.
The trial judge said the same thing in 1985.
The CoA judges said the only thing that is important is that Jeremy Bamber admitted to being able to enter and exit the house via means other than the doors.
What window he entered and exited from is not legally relevant.
So a new catch on one of the windows does not affect the case in any way.
Jeremy Bamber has a history of lying about non-disclosure of evidence.
I very much doubt any such statement was withheld by the prosecution, given Bambers history of lying on these matters. It's just one more lie.
But if there was non-disclosure in this matter, then it will be of no consequence whatsoever, due to what the trial judge said at the time, and what the CoA judges said in 2002.
If there was non-disclosure, then it would have to break the laws that applied at the time, and there would have to be evidence that the law breaking was deliberate, rather than accidental.
Even then nothing will happen, because the catch is legally irrelevant to the case. It is of zero consequence because the trial judge effectively set a precedent in 1985 when he said that the method by which Bamber entered the house does not affect the outcome of the case.