No, an 18-carat nib on a 145P does not necessarily speak against authenticity; writing instruments from the French market are factory-equipped with an 18-carat gold nib. The internet dealer presumably sourced the goods via French supply chains, or the nib was later regularly exchanged. Since the 145 does not exist in a Solitaire version, a model confusion is ruled out. The other authenticity features — magnifier star, belly band with 'Montblanc Meisterstück Pix', clip engraving with serial number and 'Germany' — fit an original. A counterfeit is therefore unlikely.