I don't think bushy is talking about a clause after the player has already moved.
In his example we would sign Milford for the 2015 season on say the 1st of November 2013. We as fans could jump up and down with delight but due to the NRL not recognising the contract or approving it or whatever until round 13 in 2014, Milford could at the start of round 12 or earlier in 2014 tell the Broncos he has changed his mind and will stay at the Raiders.
I believe this is what happened with Josh Papali and Parra, and why we were all so desperate for round 13 to start with Corey Norman as we did not want the Broncos making a last ditch attempt to keep him.
It's got nothing to do with moving.
Milford could sign with Brisbane on November 1 this year, between he and his manager say take that bit out about round 13 next year I am happy.
Many players do.
Papali didn't remove it.
That's my point- you don't have to have it.