Old Approval Notice

[groovypash]

I have recently changed jobs & received a new approval notice. Now my current employer has initiated the PERM process. Will I need the previous employer approval notice at any time. My previous employer won't give me an experience letter until I submit the old Approval Notice. I have a attested copy though.At any given point during the green card process do you have to produce the orginal documents to a US official. Will the attested copy help me?
Help!!!