I think this time its been southern railway which has run most of the special trains to Calcutta and north east. Evn they seem to have realised by looking at regular calcutta and guwahati bound trains from kerala that there is not much point in having sleeper coaches in any case with unreserved passengers occupying reserved coaches and coaches carrying twice the number of passengers than its capacity ! So its better to have a train with more general coaches and second sitting.!!.