You might want to take a look at Eurocontrol's guidance Mode S - Flight Plans and Transponders. Flight plan correlation is on the basis of Flight ID, not the 24-bit hex code.

OLNEY 1 BRAVO's SBS box receives all 1090MHz transponder broadcasts from aircraft in range and view of the antenna. Some of these will me Mode A/C replies (useless) and some will be mode S replies (containing 24 bit aircraft address, TCAS coordination and other bits and bobs). The rest (and most important ones for the SBS to be useful) are ADS-B broadcast messages of aircraft position, velocity vector and Flight ID. Flight ID is the ICAO callsign for that flight, or the aircraft registration in no callsign.

Certainly in the UK, if you are Mode S elementary or enhanced capable, the Flight ID must be entered correctly by the crew and there are AICs regarding this. Airlines should have SOPs for the flight crew.

As stated, there is no link whatsoever between Mode S aircraft address and Flight ID, and the flight crew have no access to the Mode S address, except on some military special installations.