Apparently Butcher signed for 2016-2018.
If the June 30 rules still apply U20's , then Souths can still resign him before June 30 2015 and result he legally renigs on the Rooster contract.
Means Souths play him in 2015 and can redetermine his development potential , both at Ball level and then into U20's. If he continues to be as good as expected , Souths can reassess their contract offer to keep him.
If above option true , then the Rooster signing is perfect. Why ? because if Nat Butcher continues to impress , no other club can offer him a contract. Roosters have him signed , Souths have him and can lift their offer. No other clubs can come into the dealings. If he does not live up to expectations or Souths see better options, they can allow the June 30 deadline to pass and he goes to Roosters. Ball is in Souths court , unless , Nat Butcher is pissed off with Souths.