Here are answers to your questions
1. Your Iowa address is your mailing address and practically you can maintain your mailing addres in Iowa for as long as you want to, but it is better to inform post office with your forwarding address immediately when it is known. So when you move to Missouri immediately give a change of address to post office so that a) all your future mails can be forwarded to you, b) when your cards are mailed to you, post office has your correct forwarding address that they can provide to USCIS.
2. AR11 does not change address on your case, it is for DOHS records only. For all that matters your address on your case should have been changed by USCIS with the information from post office.
3. Yes you can safely state that you're a permanent resident
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Here is my story that I would like to share with you for your comfort.
I lived in MI on address A when our 485 was filed. We moved to Address B in MI, at this time I filed for 2nd EAD / AP for spouse, Son and self, so got the address changed on the case via attorney. Then I moved to address C and applied for 4th EAD / AP for family and self, this time (somehow) USCIS changed address for me in their records but not for wife and son. EAD and AP for me were mailed to the address C and to address B for son and wife (INS forwarded these to us after receiving back from post office).
Secondly, I recived Biometrics notice for Self on my address C and Biometrics notice for wife from attorney (as it was sent on address B and post office returned it, later I received this notice forwarded by INS after receiving it back from post office). For my son I received two Biometrics notices one sent to the old address B and another sent after 15 days to address C.
So at the time of Biometrics collection I ensured that addresses on all cases Son, Spouse and self are latest (USCIS updated addresses in front of me).
Finally, on July 10 we moved to a new address in CT, I put up a forwarding request to post office immediately. On July 22nd our cases (Son, Wife and self) were approved, and on July 26th cards were mailed.
This time I called up USCIS to change my address and got the response that I cannot do it before 14 days.
Now, on August 2nd I received approval notices and card for my son and self (originally sent to address C, returned by Post office and forwarded by USCIS). But, my wife's approval notice and card were still missing, though the online status said USCIS has mailed it, my attorney confirmed that she has received copy of approval notices.
Finally yesterday I received my wife's card too, it was mailed to address B (inspite of changing address to C at INS office), and since it was over a year when we moved out from address B, post office sent it back (probably without forwarding address information), and USCIS dug into the related case (mine) and sent the card on the most recent known address (that is address D where we're currently staying).
Phew! it was a long story but Moral of the story is as long as you have your latest address known to post office, USCIS will trace you and send you your documents.
Thanks
