One of the threads that Linda posted a link to was my experience last March. I had many conversations with the higher-ups at Guest Services and was told that even if it says "guaranteed" it is not truly "guaranteed." It just has higher priority over the "requests." Because on a given day, there might only be 25 connecting room sets opening up, but 27 "guaranteed connecting rooms for families" ressies checking in. 2 of those families are not going to get their "guarantee."
I know, I was shocked that we had to fight so hard to get put in rooms that had just been fumigated for lice (they were taken out of the inventory, but re-opened because we insisted we needed rooms.) I sort of assumed that if they didn't have the rooms for us, they'd find rooms elsewhere on Disney property. For that stay, we were sometimes 2 adults and sometimes only 1. Now we will book offsite if we need to do that again. If there are 2 of us adults, we book connecting and hope for the best. Otherwise, we'll split the kids.
My point is to make backup plans if you are depending on connecting rooms.