Ben,
Thank you for the interesting reply about pocket watches. I have several, but none with a glass back, although I have seen it. I'd assumed, however, it was a later addition, because it was a screw-on glass on a standard case rather than a snap on under a hunter case as you describe. Do you know was it ever the custom to sell pocket watches to the public witha glass back? I've seen the movement presentation tin you talked about for sales to watch companies, but what about visible movements as a sales pitch to the end user of a pocket watch?
I had in my original post been thinking about glass backs on wristwatches, although I realize I wasn't clear on that. I'm still curious to learn about that, because it does seem to be a recent feature, and as Colin notes, it would be interesting to know if it was the foundering of the mechanical watch industry in the '70s that precipitated the feature, did it emerge after the resurgence, or even did it exist at the dawn of the wristwatch? Obviously, decoration of movements had been going on pre-wristwatch, so a reason to proudly display a movement was there, bit what was the impetus to take it public?
Whatever the case may be-- pardon the pun!-- I'm also curious to know who was the insightful watchmaker that began to use a glass back as a marketing element (i.e. point of distinction) on their regular wristwatch production?
Finally, just as an aside, I happen to believe that movement decoration reached its zenith in pocket watches. Maybe it is the size of the canvas and the scrolling often found, but to my eye, pocket watches movements are the most beautiful I've seen, but that's really another thread topic!