With Montblanc, a missing number is not in itself a mark of a fake. Special Editions and Limited Editions in particular often carry neither a serial number nor a consecutive limitation number. The Arturo Toscanini has neither; all that appears on the upper cap ring is the country of origin, Germany. A seller who looks and finds no number is thus describing the pen accurately.
Serial numbers in the cap ring, which every recent Montblanc now has, only came into general use around 1990, and they reached the special editions issued in support of music and the arts later still. Collectors count the John Lennon and the Bach among the first pens in that series to carry a serial number, and the Brahms has one too. Whether individual earlier issues such as the Leonard Bernstein were already numbered has never been settled — as a Special Edition the Bernstein was in any case not limited and so not numbered through. The converse also holds: a number that is present proves nothing, since serial numbers and certificates are now forged as well.