I agree completely , AP is for entry back in US. The AP will be checked in India when they are returning back to US. In US at the port fo entry, the immigration Officer will stamp and return back the AP to you. They do not retain a copy with them.
You are issued 3 copies of the AP, becuase ususally we apply for a multiple re-entry and that's what it mean. In a year's span you can travel on a AP 3 times.
I went and cameback in May of this year. The immigration officer never retains a copy. Afetr you comeback you ahev to maintain all the AP, the one that you used as well as the otehrs that you have not used. When you go for your I485 Interview, the Officer will ask for all these documents and you have to submitt those.
Hope it helps, I am not a lawyer ....
Priority Date : April 2002
I-140(w/ substitute labor)/ I-485 / AP / EAD (Myself, Wife, son)
RD 10/06/04, ND 10/08/04
EAD (Myself and Wife) AD 12/04
AP(Myself, Wife, son) AD 12/04
I140 AD 06/08/2005
FP(Myself and Wife)11/04
Biometrics-Code 2 (Self, wife & Son) 8/4/2005
2nd EAD (Wife) AD- 11/2005
2nd EAD (Self) RFE-11/2005 AD-01/2006
RFE on I485 09/20/2006
3rd EAD- AD 01/21/2006 (Wife)
3rd EAD-11/07/2006 (Self)