I submitted:
1, a simple letter stating that my PD is not current and I am qualifying for a 2-year EAD;
2. a copy of USCIS 2008-6 undate for information of issuing the 2-year EAD (you can search the USCIS website for this update;
3. a copy of your last EAD approval and your one-year EAD card.
I got my 2-year EAD card in about 10 days after they received my materials. I
Good luck,