How to change Based on Date in lot master revision

Work order XYZ is for a an output part number (70200769530) that uses the "least active ingredient" functionality to establish the expiration date of the output lot number.

The expiration date for lot A was calculated to be Dec 8, 2017 based on the components earliest expiration date of the active components.  Unfortunately a mistake was made and the incorrect lot was reported as being used.  The correct earliest expiration date based on the material that was really consumed should have been Nov 10, 2017.

I would like to update the based on date and expiration date for this lot master to be Nov 10, 2017, but the Lot Master Revisions screen will not allow the update to an earlier date.