Targons brace wont execute minions under 200 health anymore on thresh. Don't know if this only happens on Thresh cause hes ranged or what. Targons brace will only share gold if you actually last hit the minion, not execute it with true damage. 
he hasn't been able to execute since they made the execute melee only, so basically since preseason 4. people still take it on him because the bonus on hit damage from flay or whatever it's called is enough for him to kill a minion.
Its always been like this, and its still worth it.
been that way for quite a long time, and yes it's because he is ranged. targon's only executes on melee attacks after the mess they had with double targons bot lane after the item was added.
still the best item to go with on thresh and it's not hard to last hit things with him either with his E damage.
