I was waiting for that!
Here is what I THINK they did with them. I think they poured the acrylic into a mold with the raised portions for the indices and triangle (SW & GMT). Then I think they did the 3 step paint (2 paint, 1 lum?) process, and damned if I know what kind of glue the used to put it into the bezel. But it looks to me like after they glued it in place they then crimped the sides of the top of the bezel inwards. Why do I think this?
Years ago I did have a SW bezel insert fall out in my hand. No shit. As it was in pretty sad condition I decided to restore it. I used lighter fluid to clean off all the paint, then I re-did the indices in one color, the triangle in another, and then painted it all over with the light blue. It looked really nice when I flipped it over and looked at it from the front. Then when I went to epoxy it back in and as soon as I put the glue on it all the paint ran off it onto the floor. <heavy sigh>
So, I cleaned it all off, repainted it in the 3 colors and sat there and thought about how to glue it back in without ruining the paint job. I finally used Elmer's White Glue. Worked like a champ and I still have it somewhere around here.
Now, before you start messing yours up, I have never been able to get one out of the bezel since and I have quit trying.