I did an MSC cruise last year. I originally wanted to do 27 nights but they would not let me book a solo cabin. When I called, they said they had various limits for each portion and the limit for the full 27 nights was met. So I booked a solo cabin for the first 3 nights and one for the 24 nights and there was no problem with that. I even called and they gave me the same cabin too. Turns out, I changed my plans and cancelled the 3 nights anyway so it worked out better for me in the end.....