I just did this and was told by the BBTA agent that after X transferred over my reservation, it was best to call BBTA after the transfer was confirmed as they have to do an additional step to pull the reservation in. We booked directly with X instead of BBTA because the rooms we wanted that showed as available on X's website weren't showing up on BBTA's website. Also, we are traveling with our kids, and did not want to pay the extra $ for the beverage package that is automatically included in BBTA's price. So we were able to book cruise only for kids, and then transfer over to BBTA to get the shop card. Also wanted to add that we have been very happy with service provided by BBTA - they were able to reprice the cruise for us when it dropped with no issue, plus they have agents availabe 7 days/week.