As has been mentioned its as a result of similar callsigns. BA flight 803 may be called BAW6DF.
For at least the last 3 years Eurocontrol has had a Callsign Similarity team working on tools and processes to reduce opportunities for aircraft of similar callsigns being in the same airspace at the same time.
They have a tool, CSST, that looks at schedules, routes and highlights potential similarities. They also run a user forum on the subject made up of member airlines.
The tool isn't public but can be seen on Eurocontrols public site under the Resources tab.
https://www.public.cfmu.eurocontrol....pec/index.html