No reason for apologies, I always can be proved wrong.
Since I am a born West-Berliner and old enough to recall these times, I would like to play correctly, actually I´m serving polish airports from TXL in JET AGE, which in RL only happened a few times in the opposite direction, because polish aircraft were kidnapped and landed in THF....
In RL West-Berlin was only served by PANAM,BEA and AIR FRANCE in the beginning. Later followed some other British (LAKER) or American dominated (MODERN AIR,early AIR BERLIN) to serve holiday traffic.West-Berlin only could be reached through 3 air corridors all leading to West Germany, flight altitude restricted to 3000 ft, always guaranteeing a bumpy approach.
East-German INTERFLUG mostly served socialist countries including Cuba and Vietnam from SXF. Some West-European companies also served SXF, like ALITALIA,SAS,AUSTRIAN.
So situation was more complex than I asked to reflect.If it´s too much work, it won´t be done and I can live with that,too.