My colleague, 54, had cholecystectomy for sludges in his gallbladder, but after 45 days of the surgery, he experienced sudden abdominal pain, stone was seen in his bile duct. it was removed with ercp. does it indicate a newly formed stone?

I would think the stone was likely already present in the biliary tract (liver or common bile duct) but not inside the gallbladder before the cholecystectomy but it was not detected by imaging test(s). 45 day duration is not long enough for a newly formed stone to the size with symptom. The pain he had before could be from this hidden stone rather than from the gallbladder.