The reason that they are wanting the signed contract in hand even when it's already been filled is to provide an audit trail more internally then externally to help prevent (or catch) slight of hand speculation.  A grain originator could work a little float and make his bids always quite a bit better then anyone else could do....as long as he kept 'beating' the market.   The first time he's wrong his house of cards will fall over and (depending on how long he's been lucky) it could get very ugly.  

Trust me, you WANT the people you deal with  to be looking for that signed contract.   You REALLY WANT them to.