It would fail surely anyway, unless they’d apply the building standards of the time to it, which I can’t imagine they would? So they’d be applying modern 2023 regs to building work from the 1980s, and nothing built in the 80s would be up to those new standards would it?
I wouldn't be worrying about it, trying to get retrospective cert will be a headache and pointless if its been done 35 years ago imo