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A man is found in the desert, dead. In his hand is half a match. How did he get there, and how did he die?

The main difference being that here we have virtually complete agreement, whereas no two people agree on what constitutes vintage.
What, two people can't agree on what constitutes vintage? It's written on, like, the 3rd page in the watch collector book...I quote,
"Watches and pocket watches from before 1900 are considered antique. A watch is vintage when it's over 50 years old but less than 100 years."
Takes care of that issue, now back to the pre-moon problem.
The word "premoon" is imprecise. There are really two possible reasonable interpretations: "premoon caseback," i.e., before the moon was mentioned on the caseback, or "premoon landing," i.e. made before the moon landing. On its own "premoon" to me means before the existence of the moon. In which case no watch is premoon.
Let's all agree to keep it simple and agree, any Speedmaster manufactured prior to the moon landing, 7/20/1969, is a pre-moon Speedmaster.
Somehow I don't think you're going to get a lot of support. We are taking about whether a particular model is a pre-moon model, not whether an individual watch is pre-moon.
As I constantly tell my kids... you are being too literal. In so many things in this world, we don't say the whole expression, we leave out a word or two, for example: "Levi's", but what we really mean is "Levi's Jeans", or maybe, in sports, "The Sox played great yesterday". but what we really meant was that the Boston Red Sox's had a good game. Let's all agree to keep it simple and agree, any Speedmaster manufactured prior to the moon landing, 7/20/1969, is a pre-moon Speedmaster. And screw the freaking caseback, no pun intended.
Can't we just get along.
In both the examples you give there is a well established underlying phrase associated with the shortened version. The problem with premoon is the underlying meaning is unclear. Otherwise this thread would not exist. As a mathematician I prefer precise language.
Also, @Dan S is clearly correct. 😝