For ATC purposes the flights officially operate under the designator of the airline operating the flight. So for example the STN flights are mainly under the VIK designator at the moment although this is subject to change very shortly.
Passengers tickets have SCY, and providing the systems have been setup and are working correctly the SCY flight numbers should always show on the screens / teletext as well as the VIK flights. This is not ideal, but is a practical workaround which works! This goes some way to avoid confusing the SLF.