If user creates a SO and WO for  product #123 Rev. A qty of 15.  Transfer 7 into FGI leaving a balance of 8 in process.  Creates a packing list and invoice for 5, leaving 2 in FGI and 8 in process.  Creates an ECO to change the revision from A to B.  The SO and WO update to Revison B for qty of 8 that was in process.  The qty of 2 in FGI remain at Revision A and will not be affected by the ECO changes. 

The user has the following two options to choose from in order to be able to ship the qty of 2 remaining in FGI at Revision A:

1.  Create a rework work order for the new revision, and a shortage for the old revision, rework as necessary, and then place in FGI again under the updated revision.

OR

2.  They can do an Inventory Handling Issue for the old revision, then receive the new revision back in.  This assumes there is a very simple and non-functional change to the updated revision.