I am right in the middle of this process, booking 8+ rooms for a 50th High School reunion in June 2025.
I called the group sales office. What they did was book 8 interior cabins JUST as placeholders, then gave me a group number and I named the group. I was able to get the information that there were several balcony cabins available, side-by-side in the area we had decided on.
My classmates had/have until 8/9 to join, but most of them called the group office right away, gave them their information, picked the cabin they wanted and paid the deposit (fully refundable until 4/25) and we grabbed all of those cabins.
Because I had set it up, I receive email confirmations of their bookings from Carnival.
We still have until August to add to the group.
I believe that if you DO book 8 cabins, you get one free, and if you book 16, you get two free (they apparently average the cost of the booked/paid cabins to determine the class of the free cabin).
Since it's kind of weasel-y to take the free cabin, I'm 'hoping' that instead of that, we can substitute perks instead (specialty restaurant credits, excursion credits, that sort of thing), but I have no clue if that is possible....