Gogetter, did you use a TA for the booking? If so, s/he may be able to help. I've found that cruise lines won't talk to booked pax directly if a TA was used.
If all else fails, make the dining room your first stop to check your table assignment. If it's not what you want, then go to the maitre d to have it changed. You might have to change dining times, though.
To answer your question about cross-referencing booking numbers to ensure a group sits together -- yes, that can be done, and often is. We are doing that right now, actually. Our cousins are joining us on Infinity, and they used a different TA than we did. Our TAs are taking care of it. All they asked for was the booking number of the other party, and it should be all set. We've done this before with no problems.