If we have a callsign confusion ASR (Air Safety Report) they are then allocated an alpha numeric callsign. We do not take into account any other carriers callsigns unless they are reported as a possible conflict by ATC.
I'm having trouble getting my head around this.
For example, last Saturday at Heathrow alone there were 109 BAW movements where an alphanumeric callsign was used in lieu of the commercial flight number.
Clearly we're not talking about each of these 109 callsigns having been generated as a consequence of a previous Air Safety Report.
When you say "reported as a possible conflict by ATC", that seems to be a failure in the system if it has got to the stage where an ATC unit is working two flights with confusingly similar callsigns at the same time.
Surely there must be callsign coordination taking place at a higher, wider level - isn't Eurocontrol involved ?