We are signed up for this great trip in Spring 2025. Info says "guests arriving early may enjoy a self-guided visit to Versailles (Subject to availability)". I know this was available on the tour some years ago, but I have two questions. One, does this wording imply no charge, but more importantly, we're concerned about "subject to availability ". We'd like a bit more certainty, even if we have to purchase up front before we go.