US Immigration from Iceland

Should we put N/A in blank spaces on the N-400 form or just leave them blank, unless the instructions specifically say otherwise?

Hi Everyone,
My husband was approved for the oath ceremony last month following his citizenship interview. They told us it would take up to 2 months for him to receive the letter, and we're still within that time frame. However, as of Monday, I can no longer pull up his case status online. When I enter in the receipt number, we only see the image of "my" with the scrolling lines and no updates. Does USCIS close out online case status once they issue an oath letter, is this a bug, or should we be concerned?

Thanks!

Hi everyone. My status changed to "interview was scheduled" on 6/12. Then on 6/24 status changed to "document has been sent". I called USCIS today and apparently the letter was returned undeliverable and resent from them on the 24th. I'm almost certain they sent it to my previous address and mail forwarding has expired. I still haven't received the letter and am getting very concerned. What should I do?