I would have thought it didn't do much good for the testimony of a witness in its entirety if he is conclusively shown to tell lie either to the police in a statement
We are miles of into a rabbit hole of hypothetical here but:
If there was corroboration that wouldn't show him to be lying at all.
The defense would say: "At decades distance he had no recollection of the complainant, but now the police have checked his phone it turns out at the time he said she was really into anal."
Those two things are not contradictory at all.
Academic because I think he's completely made it up and there is no corroboration.
But again, trading credibility for evidence pointing towards innocence on one of the most serious offence would still be a good trade.