Stick with your gut feeling because I think you are right. You still have a lot of stones just "dying" to come out.
I can't give you an answer as to why you didn't see any stones with this flush. Maybe it was not taking the Epsom Salts ...maybe not. I just don't know.
The best thing to do would be to put this failure behind you and move on. Plan your next flush and post your positive results!!!