Just to clarify by what I mean by an "add-on" audit, that would typically be for things like new products, new manufacturing processes, new building and/or change of location, etc.
If the timing doesn't allow us to fold our required oversight activity into a recertification audit, we could bolt on the required additional time onto a routine surveillance audit, or perhaps do a special out-of-sequence audit.
(At SGS we call those bolt-on jobs 'Extension To Scope' audits, even though sometimes the text of certificate doesn't actually change. For example, in the case of a change in sterilization supplier and/or method, that's a significant change requiring our oversight, but the certificate would still say "sterile" at the end of the process).