 The fact that “Some athletes smoke” implicates  [5b]  in some contexts and  [6a]  in others shows that neither is a conventional implicature in Grice’s sense. Having more than one GCI is compatible with them all being conventional in the broad sense. The word bank has several meanings in English, including “row”, as in bank of switches. So it is conventional to use bank to mean “row”, even though this cannot be described as its normal or default use.