Slight puffing seems to happen to almost any old cell. The difficulty is defining what is too much and how dangerous it is. I have never seen good data about this, it's all hand-waving, even among experts.
With hard-cased cells like 18650, you just can't see the internal pressure rise equivalent to this "slight puffing". When the pressure rises too much, the safety went (CID) disconnects the internal cell from the terminals, so the choice is made for you and the level of "puffing" hidden.