Need to change Valid if formula for add and edit.

[Pramoth]

When i'm adding a new record, provided valid if function as below.

[_Thisrow].[Prod. Qty]<=(Lookup([_THISROW].[Job Ref],"Job Tracking upto Frg","Job Ref","sum Quantity Cut"))-(Lookup([_THISROW].[Job Ref],"Job Tracking upto Frg","Job Ref","sum Quantity Frg"))

But after added a record, when I go to the edit mode, it is not allowing to change the value because the the above validation showing error due the added record also getting calculated. 

I need a solution for different validif function for both add and edit.