What have I done: Constellation 168.005

I apparently deactivated the Breathalyzer from my online auction browser, because I took a runner at this 12-facet* dial Constellation with a few not-good photos of the dial and none of the movement. It came today and, I don't know: it looks pretty good. Opening up the caseback was harrowing because I absolutely couldn't get the springbars out of the lugs, and the endlinks to the bracelet effectively wedged the caseback in place when I unscrewed it. (Getting it back on was even more nerve-wracking; I ended up having to bend the endlinks far enough so I could set it on the threads; while trying to get the bracelet off, I perforated my fingers in several places with my thinnest springbar tool and probably need a tetanus shot now. I'm giving up on that upside-down link for the time being as well.) My research seems to indicate these aren't the right endlinks for this case.

I only got a few shots before going back to work, but am I overlooking any obvious problems with this watch? I don't have any other watches with as nice a dial. The serial number dates it to 1964, and if that marking on the caseback is "51.1.31," as I think it is, that would indicate a service in 1974. I'm not sure there even were felt-tip markers in 1974, and if there were, it's hard to believe a scribble from 45 years ago would look like it was written yesterday. The innards definitely don't look like the watches I've run across in Japan, which usually show their age after a few decades of boiling summers. I like this watch—what am I missing?

* Maybe you fellows know that in Japan, "pie pan" means something totally different, which you don't want to Google, please trust me on this.

Nice looking watch, congrats!

As far as I can see you done very well: Very clean dial, very good case, hands, serial OK

Usually a yellow gasket shows that the last service is very long ago or unserviced but movement looks excellent.

570 end links are correct for a Connie BOR as far as I know...

Thank you. I was around in 1974 too, though at five years old I'm not sure how discerning my observations of writing implements might have been. If that 5 is actually a 3, that would change the date to January 2019, but it looks completely unlike the the second 3 in "31."

There's a much fainter stamp that looks like "B C V" with a "3" underneath. My understanding of watchmakers' notations is that it's basically alchemy, but the wizened guy who services (and rolls his eyes at) my treasures in Tokyo might have a second opinion.