We got GC in July but my son got interview in November.

We got GC in July but my son got interview in November. He received his GC this month.

Officer will ask you for more information they don't have on file. You can follow the instruction as notice listed.
Be sure to remember the first name of the IO (interview officer). You may need it.
You may ask IO to check what document they really need for your GC. It depends on the interview situation. Good and positive communication sometimes can help.
Be patient and business dress.
No cell phone, security check like airport, be 5-10 minutes earlier than the scheduled time.
Short and clear answer.
Be polite.
Don't worry too much if you don't bring the required document they really need. You can go back home and send it back to the IO once you find. My son forgot his one document and came back and sent it back to IO in the afternoon before the IO left (the IO interviewed my son has work hour from 7:00am to 3:00PM).

For your references,

Good luck!!