Yes. On the Leonard Bernstein Special Edition neither the fountain pen nor the ballpoint was given a laser-etched serial number. On this edition the absence of an identification number is therefore neither a defect nor a sign of a fake, but standard. Later editions without a laser-etched number appeared from time to time as well, Noir et Noir and Rouge et Noir among them, while the Bohème editions that followed carry a serial number again. A missing number is thus a warning sign only on models that demonstrably ought to have one; there it usually points to a replaced cap.
Montblanc will issue a certificate of authenticity after the event on request, though no longer free of charge. As of 2016 the sums quoted for this ranged from about 50 to 61 euros. Anyone buying a pen without papers should allow for that amount or take it into account in the price.