The PL would have to prove that the two parties were related on the balance of probabilities. That wouldn't be easy in the first place, but what is the effect if they can prove it?
There is no legal requirement for the accounts to show related party transactions at fmv, so it would make no difference to the main accounting statements. There is a requirement for a note disclosure, though, so readers of the accounts can make their own minds up. No-one is getting a points deduction or going to jail for a disputed note disclosure.
The PL rules, though, do allow the PL to restate related party income to fmv and so the later inclusion of a related party transaction disclosure may lead to a correction to the club's FFP results.
I still think this is maybe what the PL is looking at, although others disagree. I think Herbert's "understanding" and the shift (if it's not nonsense) from fraud to complexity supports that.
I think that is all right, but it's just my opinion and may all be bollocks, of course.