No. Not every genuine Montblanc nib carries the emblem familiar from the catalogues on the nib face. In the simpler ranges of the 1960s and 1970s in particular, sparsely marked nibs were fitted that show little or no engraving beyond the gold designation. On those models such a nib is the correct factory fitment; a missing emblem is therefore evidence neither of a later nib swap nor of a fake.
The uncertainty usually arises because model surveys mostly illustrate Meisterstück models and more recent ranges, all of which carry the more elaborate nib engraving. In judging an inherited or second-hand pen, then, what matters is comparison with photographs of exactly the same model from exactly the same period, not a glance at today's range. In any case, whether a nib belongs to a pen shows less in the imprint than in whether nib and feed sit cleanly in the section without a gap.