There aren't really any significant discrepancies, the mix up over the front and back doors is easily explained since the interviewee didn't want to admit that they had left the patio door unlocked and consequently the apartment unsecure.
IIRC - Gerry had already 'admitted' the patio doors were unlocked when he said during the interview that Matthew had entered 5a through them.
IMO Gerry did not 'change' his statement - he
corrected the misunderstanding which had occurred between himself, and/or the interpreter/ PJ officer as to which door he was referring to when he said the 'front door'.
There was considerable confusion during interviews because of some people calling the patio door the front door and others calling it the back door.
If there had been anything suspicious in the explanation Gerry gave as why he corrected his statement - then his reason would have been recorded and Amaral would have mentioned it in his book.
IMO it would more a case of the PJ not wanting to admit an error had occurred during interviews with their interpretors/PJ officers - although personally I would have no criticism of that at all. It was the first interview for everyone concerned - and therefore extremely understandable IMO if misunderstandings happened.