This is where I have preached that people need to change their thoughts… There are two dates in the Order Release… need by, and ship by.
the Need by is what the customer wanted
The ship by is your “current” promise date. It is what drives everything… MRP will ALWAYS drive to this date. If your jobs do not meet this date, then MRP will try everything in its power to make it happen… if you lock the supply date/quantity, MRP will then tell you to make more. it is the way Epicor is designed.
My additional suggestion (and ongoing enhancement request) is to add a THIRD date to the sales order called “Original Promise Date”. This would be the date that you initially promised. It is what you would measure performance against. It “never” changes, unless the customer requests the change, OR unless you ask the customer if you can change it, and they agree to the change.
The SHIP BY date should be flexible, and should be adjusted whenever the supply cannot meet the demand.
(ok… i will step off my soapbox).