if there was going to be set changes then would they not have already started for the one year birthday??
It only tales a few days to change a set.
You mean "it only takes a few days to
physically
change a set". The actual planning, design and manufacturing takes months. As well as the basic aspects of the set (sofa, table, walls, windows, flowerpots), there are several major issues - sizing, routes through the studio, camera angles, camera movements, lighting, facilities available in the studio - which all need to be discussed, planned, and accounted for before the first piece of set is actually built, and long before it actually gets put into the studio.
It's not a case of "aah, don't like that, we'll change it. Let me load up Sketchup and design a whatjamacallit-whosmebob and then well get it in for tomorrow morning".