Why is the magnetic variation value from 1999, although the AIP Charts in my country are up to date? In all of the chart examples I shared below, the variation value is 3.2°E and belongs to 1999. According to my research, the current variation value of ADANA LTAF airport is 5° 46' E. The year the charts are published is 2021. In addition, the variation value of 2017, 3.5°E, is shared on the airport chart. Why are all these values out of date and not fixed? Why is such a way of sharing followed in the charts? Any ideas?
Because the magnetic declination in a given area changes slowly over time, as little as 2–2.5 degrees every hundred years or so, or by 1 degree every three years in locations closer to the poles. Depends what part of the world the map covers. Not many airport facilities close to the poles.