your conclusion only olive oil works for you might be right or not. Looking back to my flushing period I realized sort of a stone stop beginning with flush 7 or 8 (don't remember exactly).
To my great surprise all the following flushes were quite productive and as a matter of fact, while three more or less stoneless flushes gave me the impression of being stone free flush number 14 yielded 2.400 (!!!!) stones.
So the fact that you did not get stomes might reflect that your liver was simply not ready by the flushings time to let stones go.