According to JoeW, who once sent me an unsolicited email about NS Meyers, is that they actually employed multiple manufacturers for their insignia and that is why you tend to find so many different styles and placements.
I suspect that for this reason, many of the different styles overlap rather than precede each other in order.
I think that too many collectors try to think about these things in a linear fashion with nice clear "demarkations" between wings and patterns. "Pre-war, early v late 30's, 20's vintage, early WWII, late WWII, KW-vintage Frankly, I think many of these are artifacts of what people what to think rather than what is really the case. It's almost like the collectors want the manufacturers to have said -- "Well, the Japanese went and did it now, lets go make new dies now that WWII has started!".
Broadly speaking, the NS Meyer Adam's style USAAC wings (pilot, observer, balloon, airship, etc) all are probably all from the 20's and 30's. The USAAF Pelican wings were probably made from WWII (lets just say circa 1942 when all the new ratings were authorized) all the way up until the cold war. The USAF wings with the alpha/numeric wings were made from the late-50's/early 60's until NS Meyer went out of business.
USAAC wings in the Adam's design seemed to have just used the shield (~1919 to 1942). Pelican wings used all sorts of different variations and placements (1942-1960). Alpha/numeric used letter/number (1960-current). There are probably exceptions to this rule and a fair amount of overlap. With NS Meyer, their is almost always exceptions to this rule and overlap. Frankly, trying to "date" a wing to any more than these broad time periods outside of a "biographical wing" is (IMHO) silly.
IIRC the first wave of NS Meyer restrikes started showing up in the 80's (in some of the harder to find ratings--balloon, TO, airship). Made by NS Meyer for the collector market, they were made with the original dies and had the "wrong" pins. Since that time, there seem to have been multiple other waves of restrikes like the alphabet wings (they had wrong pins and also a shinny black glossy finish on the back).
Since then, you see other NS Meyer-like wings to fool collectors, like NSM wings with the hallmarks removed (and not infrequently with a fake hallmark added instead). You see wings where the "wrong" pin is removed and replaced with a vintage wing. One thing I don't see is where the pin and catch are removed and replaced with a clutch back.
Finally, B17 John is spot on, there really isn't much proof other than general observations and specific biographical wings that can be used to nail down the date of when these were made (much less sold or worn).
Sill, no matter what, as a collector you have to decide on your own about NSM wings. I can promise you that no matter what, 3 people will say one way and 2 will go the other.
Edited by pfrost, 31 January 2016 - 01:41 PM.