ME22n BADI - delivery date problem

HI I am working on a BADI for ME22N -- > IF_EX_ME_PROCESS_PO_CUST

When user adds a new line item I need to track it.Is there any variable or table field which gives information that the line item I am refering to is a new line item user is adding and not an already existing line item.

Eg:Once user ads a line item it should show a default delivery date on screen in the delivery date field.But if user changes the same line it should accept the new delivery date and show that on screen.

If user edits an already existing line then it should show the date edited by user.but if user adds a new line then the date is got from the DB.

I need a field or flag in BADI which tells me that the line item is a new one or an already existing one.

Regards,

Shital.