The postal service is not supposed to forward INS mail
I spoke to an IIO back in October. No INS mail should be
forwarded (if it is, it is an error). Instead it must be returned to
sender. I had my EAD returned to sender even with the correct
address (we have a mail slot, not a box, and our apt. # is not
easily visible).
The (very helpful) IIO at VSC told me you should change your
address in writing (although they can take them over the phone,
they need documentation as well), preferably with the relevant
form. The form is now compulsory. You must send this in as
near your moving date as possible because they might
adjudicate your case very near the day you move and do not want
a future address.
It is also an immigration violation to not notify the INS of an
address change within 10 days of moving--even after you receive
the green card.
Hope this helps. Please do not leave anything to chance!
Good luck.