So, in my nightly browsing for vintage watches, I stumbled across what a dealer described as a 1950s Longines 13ZN. I looked closer, and to me, it didn't look like it was from the 50's at all. I would've guessed the early 40s. And then, I looked further still, I saw that there was a singular pusher on this case at 2 o'clock, and nothing at 4 o'clock. This was a mono-pusher 13ZN. I sent an email to the dealer, who was a large European seller of both old and new watches, though one I've never dealt with either personally or professionally. I didn't hear anything back for one week. I sent a note via the contact form on his website, still nothing. I was about to give up.

I sent one last email to this dealer from my personal email account and the next morning, I heard back from someone at the shop. They answered my questions about movement and case numbers, condition, etc to my satisfaction. I then took the information they had provided me and did quite a bit of research. I first looked at John Goldberger's book on classic Longines watches (you can see a pictorial display of it here) and saw that 13ZN mono-pushers did not account for many of arguably the largest collection of rare Longines in the world. That confirmed my suspicion that this watch was rare, and very likely, early. Then, I reached out to Longines to ask what information they might have on the watch. Longines has one of the most active heritage departments around, and if you send them a note with your movement and case numbers, they usually get back to you within 24 hours. It's an amazing service available to all.