Let's clarify that there are not required vs non-required fields. The asterix indicates a critical field, meaning if that field is not completed, you cannot submit your filing.
The expectation is that if the bank has access to the information requested, it is to be reported. The RSSD number is easily accessible (it's a few clicks to look it up on a website), therefore, you should be reporting the information.
Now, should you go back and amend all of your previous CTRs? Your best bet would be to call FinCEN and get a "ruling", then document whatever they tell you. Without FinCEN blessing your bank personally for not amending those filings, your prudential regualtor will have plenty of ammo to criticize your bank.
I can't herd the cats anymore, so I just set up the electric fences and let them fry when they stray out of bounds.