Commentary Inf XXI 39

The notion that barrators come straight from earth to this point in hell, carried off by a devil, seems to violate the rule that all must cross Acheron with Charon ([Inf III 122-123]) and then go before Minos to be judged ([Inf V 7-12]). Even the black Cherub who carries off the soul of Guido da Montefeltro is said (by Guido himself) to have carried him only as far as Minos ([Inf XXVII 124]). Thus Singleton reasons (DDP Singleton.Inf.XXI.39) that the devil at least stops briefly at Minos's place of judgement in order to allow the formal sentencing to take place. (Must we also imagine that he accompanies barrators from Lucca aboard Charon's skiff?) It is surely true that Dante is generally precise in honoring the ground rules that he establishes; it is also true that he has written a poem, one that allows him to please his fancy when he chooses.