Interesting Fulfillment Behavior, Items Not on SO

Hey All,

I have been experimenting with creating fulfillments using web services and found out that it is possible to create a fulfillment for a sales order with items that are not found on the sales order.  The reason behind this is that we are developing a 3rd party WMS system and if for some reason items can not be found from the sales order, I'd like to substitute and then have the new items upload with the item fulfillment without needing to go back and update the sales order. 

Since I am able to do this, I was wondering if this would be the best practice.  Since inventory is decremented based on the item fulfillment I see no issues there and the way our system works is that it always closes out the sales order after the invoice is created because we don't do back orders, closing out any open commitments.  The only reason I am concerned is that since we are unable to do anything like this in the UI, I hope that Netsuite will not bug out on us in the future.  Anyone have any experience with