I was a Montblanc dealer once in the 80's and 90's had a dealer book showing about 8 to 10 different engraving styles on the barrels of this pen. Each engraving was signed with initials of the engraver. So they may have been prototypes. This was 30 years ago when introduced and not sure if some of these engravings were used or if all the pens in this edition have the very same barrel engraving.

Good luck with your sale, great photography Barrie. Wish I kept mine.