Is it correct that a newly bought Montblanc Bohème Noir Platinum is delivered with a 14K nib although the website shows an 18K nib, and how does one care for the platinum plating?

In standard Meisterstücks and Bohème models, 14K gold nibs are fitted; 18K nibs are found only in the French market as well as in precious-metal variants (silver, gold). Models depicted on the Montblanc website often come from the French market, hence the deviating nib statement. Precious metals like platinum are basically resistant to hand sweat; thin platinum plating, however, can suffer in the long term. It is recommended to wipe the writing instrument after use with a lint-free cloth (e.g. spectacle cleaning cloth).