That, to me, seems the best point. A club that has conducted its financial affairs in accordance with the rules pertaining to the league/ competition in which it is participating, and has had confirmation of that from that League, should not be penalised when a different league applies different rules to its disadvantage. That is basic fairness. The fact that the club has been told that its accounts comply is what's called a legitimate expectation.
Having said that, I don't, from what has been said on here, see all of that as extinguishing the entire amount of breach, I.e. Forest would still be in breach, but it should reduce the amount and this the penalty.