"If an event changed the economic situation of a country it should be reflected anyway"
Well, a dissolution of a country + a following incorporation into another country + the introduction of a completely new currency in the affected area + a totally different economic system (capitalism instead of socialism) surely would mean "change of economic situation in a country", wouldn't it?
If a worker in former East Germany is not allowed to travel (and has no budget to do so anyways) and it completely changes from one year to another (freedom of travel + strong currency + other economic model), he would surely do so. Take my parents as an example. For 40 years, they could not leave Eastern Germany (except for Poland, Russia, Czechoslovakia, etc.). Once the wall came down, they made a 30-days trip all around the USA - taking a flight from Berlin-Schönefeld (East) to Frankfurt and then straight to New York.
Let's have a look at the passenger volumes at a couple of airports in affected areas. While Schönefeld (east) had less demand in the following years (mainly due to Interflug ceasing operations), Tegel airport (West-Berlin) had more demand
. It's not a sudden increase, but a steady one (until 2001 for some reason
So what about Leipzig-Halle (another main airport in former East Germany)? Some 275,000 passengers in the chaotic year of 1990. But already 634,000 in 1991 and 1,073,000 in 1992. 4 times as much as back in 1990!
Even airports in West Germany profited from the development as they had many connections into the "west". So people from former East Germany went to Franfkurt or Munich to get to the US (or London/Paris/Rome if the budget was tight).
Regarding the game mechanics, the question is if the airport passenger statistics are based on actual statistics from those years. If so, everything should be fine. A "world news entry" considering the "opening of dozens of countries" would be a nice idea (even if you can fly to these countries in the game well before 1990). It's not less important than 9/11. Probably the biggest world-scale change of the 20th century following WWII + separation into east and west.
This does not only affect former East Germany, but also all the other East European states. Just to mention a few: Latvia, Lithuania, Estonia, Belarus, Russia, Ukraine, Poland, Czech Republik, Slovakia, Hungary, Rumania, Bulgaria, Moldova, etc.
So...I'd say an increase of passenger traffic for the period of ~1990-1995 from central/eastern parts of Europe is more than logical and affects the whole world.