We had a loan close where the principal residence was used as additional collateral...should have been given a ROR at closing but it was missed. How do we proceed from this point?

My advice - do nothing and hope they don't rescind within the next 3 years. This cannot be corrected.

We had the same thing happen on a HELOC and we had the borrower sign a new rescission, and refunded the interest that had accrued between the date that it was put on the system and the new rescission date. We put documentation in the file so that if we were asked 2 years later we'd know what we had done.

You can't fix a RofR error once you have advanced the loan proceeds. You might provide a correct RofR BEFORE advancing the funds. Trying to "correct" the error only notifies the borrower that you messed up.