Rule 15.8 provides some guidance to this:
15.8. If a player stops play incorrectly after mishearing a call or not knowing the rules, then any subsequent play stands and play restarts with a check from the point where play stopped.
However that only helps if the team accepts they made a bad call.
Rule 1.10 helps out a bit with that:
However players may seek the perspective of non-players to clarify the rules
But there still may be a situation where teams disagree about the rules and the correct interpretations. At that point it would be up to the Captains to negotiate a reasonable outcome.
In the example you provided, they only issue is where the turnover location is, so if no agreement could be reached, captains might choose to have the location at the midpoint between the two proposed spots (as outlined as an option when disputing out-of-bounds turnover locations (see Interp. for 11.7)).
If however the claim was that the defender had gained possession by nail delaying the disc (which is not correct)and then lost possession after the disc then hits the ground, they are asserting that the defender is now the previous thrower. Therefore if there is any dispute regarding this matter, the defender would still retain possession. All this may be moot as it is likely we will look to close off the loophole that allows defenders to nail-delay in future rule revisions.