Does the LI20 background job not create a spool with the values?
Has there ever been a case that the difference was not posted finally?
Just for simplification, if it was always posted, then it should be okay to pull such list after the fact with MB51.
If this is not accepted then you have to go the hard way and develop an ABAP that reads the values from MBEW and other valuation segments like EBEW and QBEW