Pens from the 1980s with a single-colour nib and blue viewing window are authentic and correspond to the construction state at that time; comparable examples are documented at fountainpen.de/old-80er-146.htm. The marking "W-Germany" indicates production before 1989. With remaining doubts about authenticity, the pen can be sent for assessment to Montblanc Hamburg; flat-rate remote diagnoses are unreliable. On seller statements about the duration of use one should not rely, since these often deviate significantly from the actual production period.