okay....you bring up some other things now that might also add to the mystery. A 2nd hand throw away might be in that pile because it is stuffed.
It might be incorrectly pinned, have a broken spring, a stuck pin, too long a driver (top pin), etc etc.
There are multiple scenarios possible.
I have bee locksmithing 28 years almost and encountered cylinders I have been unable to pick too. It can be luck of the draw.