I was doing a search on accessible staterooms and came across this thread from a month ago. My experience in booking an accessible stateroom is slightly off topic from the OP's question. But, I thought I would throw in my own two cents as I stumbled across some interesting information that I think will be helpful to others who find this thread in the future.
In my case, I wanted to book an accessible stateroom for my parents on the Dream as well as a connecting, non-accessible stateroom. As it turned out, the accessible stateroom was indeed available to book online. But, the connecting, non-accessible stateroom was NOT available for booking online. It kept showing up as unavailable. This proved true for every connecting, non-accessible stateroom that adjoined an accessible stateroom on the ship. (The accessible room was available for booking, but the connecting, non-accessible stateroom was not). Unfortunately, my self-professed "Disney specialist"
travel agent was unable to provide any insight other than someone had already booked the non-accessible stateroom. I want to stress that the connecting, non-accessible booking was NOT available for booking online, even though I was trying to book it at the same time as I booked the accessible cabin as part of a multiple cabin booking.
Given that the cruise we were interested in booking was over a year out, I suspected that something was up. So, I called the cruise line directly and learned that the connecting non-accessible staterooms are specially set aside for booking by people traveling in an accessible cabins and they are NOT available for booking online. (The cabins are released for booking by the general public online somewhere around the time for final payment is due, if I recall correctly). Someone - myself or the travel agent - has to call in and book the cabin either after booking an accessible cabin, or book both cabins at the same time. An interesting caveat. One would think that you could book a connecting non-accessible stateroom online at the same time that you are booking the accessible stateroom online. But, that was not the case in my experience. Out of curiosity, I tried making an online dummy booking for a future cruise in late 2016 and encountered the same problem -- accessible cabin could be booked online, but the non-accessible connecting stateroom could not. I hope this info. helps someone else out.