I have an N serial on my wrist as I type, And it’s identical to this one on my wrist
https://drive.google.com/file/d/1-NK...4EJivrPLW/view
The fonts in the writing look almost identical but the hash over the 160 mark on mine and this N4 serial clearly goes further and basically covers the 160. On that piece pictured it does not....I would say if that watch was sold 1991ish it might have been back to service and got a replacement bezel late nineties possibly or maybe they had some of the zenith bezels left over like what would have come on a W,T,some U serials.....that is the same bezel as the W serial I have....