Police departments vary widely in terms of their policies about tape-recording or videotaping interviews. If you tape-record the entire interview, then it's very hard for the defense to say that you're trying to change somebody's testimony or you're shaping someone's testimony or feeding them information. The problem is, a lot of suspects that come in aren't always truthful the first time they speak to police, and so if you tape-record that, then you're giving the defense an inconsistent statement by someone you may call as a witness. Police Department's policy is to only record a summary of the interview at the end, and that gives defense lawyers grounds to argue. So I guess the better practice is, you get down to where a person is ready to tell the truth, and we're going to tape it now, and that's what's taped.
Any extraneous conversations are vagaries and forgotten things.
Here, you've got a tape saying what he said. You've got live testimony saying it. I think that's what's important, not what was not said, or omitted, or forgotten. He stuck to the same story during rigorous cross-examination. That's what counts.