You should be able to get credit for any cruise by going on the web site and requesting that it get logged.
Unfortunately, the cruise lines do have rules that forbid people of one region buying a cruise in a different region.
But rules are not "laws" so if you happened to buy a cruise through an English or American site (or travel agent) I don't see how they could keep you off the ship (but just to play devil's advocate, anything is possible).
I know that 10 years ago it was very common for Europeans to call up a US travel agent and book a cruise by credit card, but I don't know what the rules are now.
Pete is our resident travel agent here - I would listen to him first in this regard.