Yes. That's what you should

stick on! Many places take mailing dates as the cut off date, including IRS tax returns and many rebates. However, obviously USCIS doesn't take this. Now the questions is: what exactly CIS is taking. Most people believe it is the delivery date. But since CIS is making the rules, things can be complex.

However, a good thing is that some people got their 485 accepted with receipt dates after 10/1. So this should be used as a great evidence to show that the delivery date (received date) should be used to judge whether an I485 package should be rejected or not!