Sludge is not really considered 'stones.' Think of it like a 'heavy substance' that contains tiny, tiny tiny, particles that could unfortunately cause problems all by itself. It is possible, however, for the sludge to further concentrate to build stones over time.
I have sluge and my gallbladder is only working at 12% but the surgen told me i have no stones, isn't slug ting stones?
Yes, you do need the ERCP procedure to get rid of the sludge. Sludge can be 'lost' to the bile duct during surgery. In addition, people can and do form new sludge/stones after GB removal. You may want to talk to your doc about diminishing your probability of forming new stones/sludge in the future with diet/medication.