Some airports are pretty close to reality. Most airports are just arbitrarily determined based on their relative size.
Airports do grow in time, but MUC won't be at 45 in just 8 years time. So it probably needs an adjustment.
You can PM sami with the request, what the airport is, what the number should be, and the sources that provided that number (Wikipedia not being a source). He has changed many (most major US airports were WAY off before 1.1 for example) and may change MUC.