Let me chime in here as founder and original owner of Graco Awards. The brooch can be used to somewhat accurately determine the period of manufacture of any medal. There is no way to really accurately date a medal's date of manufacture by the brooch. Here are several reasons why:
1. When they are ordered on a military contract for Defense Supply Center, the specification calls for a particular brooch to be used. If a manufacturer has another type on hand, they can apply for a variance in the contract to allow the older parts to be used up.
2. Many medals are ordered from local supply activities by individual units and organizations today, rather then being ordered from the depot. In this case, the local suppliers may sell old stock, new stock, or a combination of items. For example, a military unit can use their credit card to order medals from Bubba's Army Surplus outside the main gate, and Bubba can then order medals, ribbons, and lapel pins from any supplier who has them in stock, package them in boxes Bubba has laying around the shop, and sell them to the military unit.
3. Units can order medals directly from a legitimate manufacturer such as Graco Awards, who can use any components that they might have in stock. This could allow the use of older styles of brooches or boxes or other components.
4. As far as the award date, consider this. The military depot doesn't always issue items on a first-in, first-out basis. Medals may sit on their shelf for many years before being issued out to units. I can recall my time in the Air Force when our unit, in the 1970's period, was sent decorations in the black WWII boxes, for current issue. So at least for award date, there's no way to accurately determine a date.