Given a callsign such as 'VRS1', where VRS is an airline whose IATA code is VR, this returns all possible alternate callsigns by introducing leading zeros - e.g. 'VRS1, VRS01, VRS001, VRS0001, VRS00001, VR1, VR01, ..., VR000001'

Given a callsign and an optional operator ICAO code this returns all possible callsigns that routes could be stored under, in the order that they should be searched on. This takes into account the behaviour of the VRS route compiler.