2 months is only when you apply for your first extension (based on a non-immigrant O VISA of 90 days, the one you always start on). Every successive extension is based on a 12 month statement, as they need to check if you kept you 800k for 3 months after obtaining the current extension.
then why ask the question, just take the risk. In my experience they will NOT accept it at CW. It might depend on the mood of the officer in front of you.
I never was asked to show my previous 90 days confirmation when doing my report in person. They have all the details in their system.
You will get an email reminder approximately 1 month before your next report is due. This way you'll know the date, unless you went abroad in the last 2 months.