I'm not sure if the reference here is to Keychain's "Secure Notes" or the "comments" field associated with password items. If the latter, I've found (at least on older versions of OS X/macOS) that when Safari updates the value of a changed password, it deletes the comments! I used the comment field to add the (random) answers to security questions, and got burned on a couple of sites when I've needed to do an account reset and lost those answers.