The difference is one is highly subjective, well trodden publicly and clearly time barred. The other is sufficiently serious (very) and concealed to be capable of breaching the SoL. Furthermore, it is something worth pursuing - a disagreement on RP is not and, if it was, you have failed to address why they waited 10 years to pursue and haven't pursued the ongoing "breach" all founded on the same factual background. Of course you can believe what you like but you haven't addressed any of the questions including how you prove the subject RP point, how you now demostrate the FMV of 10 year old deals with good clarity.
PS related party and FMV only commenced in the PL rules in 2013-14 so "related party" couldn't relate to any charge for any year prior to that.
Fair point about the Etihad funding, but I think you are coming at this from a different PL angle to me.
Unless I am mistaken, you think, quite reasonably, the PL came to the referred allegations based on the seriousness of the charges, the potential financial impact and there being a good likelihood of success.
I think they simply came to the referred allegations based on a list of unresolved issues arising from the leaked documents and from all the previous UEFA investigations. Otherwise, I find it hard to explain the Mancini allegation, for example, which must have a low likelihood of success, is immaterial, most probably time limited and is hardly serious at all in comparison to, say, the Etihad funding.
Tbh, I didn't address your other points because I didn't think they were relevant to my point. But if you are really interested, here we go.
You know the RP definitions. Imo, the PL will have been looking for evidence that Mansour, or a close member of his family, has significant influence, directly or indirectly, over the operations of Etihad. That evidence could come in many forms, it could have come from the investigation. Any suggestion would just be complete speculation. But it could exist and it could have just come to light recently. Less conspiratorially, it's just as likely I suppose, that the club's counter-evidence wasn't sufficient to satisfy their experts.
As for FMV, that has no effect on the accounts of course, the only change in the accounts from a change in RP designation would be an additional note disclosure. And, of course, you are right that FMV only comes into play in the PL rules with FFP. I know that. Practically, though, I imagine UEFA still have their valuations from 2014 and, presumably, 2019. But again, I am not that bothered about the financial impact. I would be more worried by the reputational fall-out. The state-owned narrative would be relentless. Actually, if I was a conspiracist, I would say that's the point. Luckily, I'm not.
And anyway, as I said, I doubt it will get that far.