Most GI items, even today, have a numerical manufacturer's code number on them. Each manufacturer is assigned a unique number. At the beginning of WWII most otems had very little manufacturers info or dates on them. Towards the of the war items had much more info on them such as contract #s, dates, specification #s, manufacturer's name or code etc.
Most items made in the last 50 years have a Defense Supply Agency (DSA) or now, a Defense Logistics Agency contract number. The 7th and 8th characters are separated from the others and tell you what year the contract was let on that item. That can help to date the approximate age of items.
Lance