I have been checking the Milano site occasionally using only the 5-digit ZIP code and last name as suggested in an early post in this thread. It always came back with no record of the submission.

Today for some reason I let one of my form-fillers complete the boxes and it put in ZIP+4.

And BINGO! The Milano site now says they "shipped" my rebate on 8/11. I still haven't seen it, but at least I know it should be on the way.

(If someone else previously suggested using the +4 ZIP Code, I missed it.)

Updated to add: The check arrived in the mail on 8/29. So 18 days in "shipping." It is interesting that I WAS able to deposit it using my phone's banking app - the app didn't like it much when I hit Submit, and appeared to be in a continuous loop, but I just closed the app and promptly got the usual email from the bank saying it had been accepted.