Have just made enquiries with Brittany Ferries & they tell me race is on 17th & 18th
Are they confident enough to guarantee you a refund if they're wrong!!

Personally I would go for the 17th & 18th as I think they want it closer to the Classic rather than further from it.
But as said before until all of the international calendars are confirmed the ACO do not formally confirm the date. Take your chance with ferry bookings if you wish (and I might do a bit later on) but don't moan if you get it wrong!!