If you purchase tickets on IC or IC+ the tickets are good until 24:00 on the specified date. If you reserve seats (second ticket) they are good only from specified date/time. You acn apply for a refund (by mail) and they only issue credits for future travel.
Have not seen a clear explanation on Eurostar.
Radiance of the Seas - Nov 2006
Legend of the Seas - Jun 2007
Costa Fortuna - Mar 2008
Legend of the Seas - Oct 2008
Celebrity Constellation - July 2009
MSC Orchestra - Jan 2009
Navigator of the Seas - March 2009
MSC Poesia - November 2009
Jewel of the Seas - June 2010