I think what RCI's shore operation told you is questionable. While I'm sure the ship has some input the truth is the shore-based staff normally controls when things like this are opened up. It is like any other company where 'corporate' likes to dictate to the regional offices (the ships). I've been on both Oasis and Allure and the one thing that impressed me was the precision they showed in keeping things organized.
However they are probably correct in that you'll still get to see the shows you want, when you want. After all, if you can't book anything then nobody else can either so all that has happened is the window has gotten smaller.
Honestly, on Allure last summer none of the shows we booked were full. Of course that is no guarantee for your cruise. But we were in the middle of summer with a ship that was about 100 passengers short of max capacity. That won't be the case for your cruise.