ISO 13485 typically does not have unannounced audits. It is a hallmark of CE certification audits, where they are often merged into a single audit.
I do not recall a central repository of outcome information, companies generally do not taut dirty laundry so it would be a biased sample from other sources.
My personal experience is that while they feel more exciting (though not necessarily more tense), the results are usually lower in grade and less in amount compared to the regular scheduled audits. It would be a lower bar of things to expect.
Won't go into further specifics for obvious reasons.