Hello! Since a lot of political things are structured in very high detail, I wanted to add a bit of info on West-Berlin:
This concerns all airports within the Berlin city limits, Tempelhof and Tegel. These were only allowed to be flown to by airlines from the allied countries (FR, UK, US, [SU]) until October 1990. IRL PanAm had a big base in Tegel, flying from Berlin to Frankfurt and other German and European destinations; Lufthansa only started flights to Berlin in 1990.
This is very different to the current setup, where the airports are no different to any (West-)German airports.
Hmm... Interesting. Would need the addition of some specialized fields in the airport database tool, then, allowing to select the precise country allowed to fly in/out (instead of just "intl / no intl").
some info on the topic: https://en.wikipedia.org/wiki/West_Berlin#Air_traffic