I'm scratching my head here as I am trying real hard to figure out how this piece has been identified as definitively being a post WWII manufactured DI. My thoughts are as follows- the type of catch is one that I have always considered to be an earlier catch than a later one. Most of the later manufactured US insignia that I have encountered that has a pin back, has had what I call a "ball" type catch. That is, the sides of the catch are rounded rather than squared. I've noticed this on rank insignia, DI's, etc. I just went through a box of about 100 post war marked DI's and I didn't find any with this type of catch. I've always considered this type of catch to be an inferior design as the roller tended to fall out rather easily. This type of catch looks a lot like the catches on Juarez pattern wings- and those pieces always seem to be missing the roller catch.
The other thing is that so often, earlier vintage DI's have a glassine appearance- very clear and smooth. The later era DI's tend to have a more opaque look to the enameling.
Personally, I wouldn't have any heartburn at all putting this in my collection and calling it WWII.