What happens if a missing attachment has gone unnoticed for 9 months of invisalign treatment? Can refinements be made?

Some attachments are more important than others. If your orthodontist
didn’t mention anything it was probably not one of the crucial once. He can
always add new attachments or remove some of the old once as needed when a
refinement is done.

Have to agree with Patricia. Some att's are more important that others, since you're in passive aligners it's not likely a big issue, but refinements can always be done to catch up if necessary.

Attachments are designed for 3 purposes: 1. aid in certain tooth movements, 2. resist certain tooth movements, and 3. help retain the aligners in your mouth during Invisalign treatment. Since you are into your passive aligners on the lower arch, now is a great time to ask your orthodontist about the missing attachment and whether or not you need refinement to complete your lower treatment. Dr. Panucci