I'm not sure anything "returned". I don't know how you would know that something returned, as opposed to just taking more time and work to free them from the liver. It's possible that you just weren't done, but assumed that you were. Notice that you never did get to the ZERO stone phase, let alone two straight with ZERO.
It's just a guess of course, but I'd guess that you were not done. You still may not be done. I think it would be hard for the body to produce that many large stones in a short amount of time. You'd have to be feeding yourself axle grease every day!