A very interesting discussion with a wide point of view.
I have collected items from WWI ~ Modern.
However my main focus is U.S. (WWI, WWII), and Japan (WWII). Basically my feelings: originality, conditions, and the *price. *: Personally don't really like judging with money, but that's part of the rule.
It's the first ever World War, when everything started to change and evolve rapidly. Anything from gears to weaponry. Some of their traits were still found on modern equipments, for 100 years ---a Century !!
The second World War and the most dramatic, catastrophic period of the history of mankind. Many great designs quality changes.
Too me, I like both mint and used conditions. Early or late doesn't matter.
Mint - How it is like not being used. Tells me the original color, shape, descriptions (labels), and the workmanship.
Used condition - Being used at the actual battle. If name is on even better. The level of wear, color, shape change, damage.
For U.S. field gears, some early war items have late war color (OD 7), some late war produced materials have early war color (OD 3), some have both colors (pattern 1943)
Let say there are two identical objects, made by the same company, same year ,however the color, shape, materials are different from each other.
So that tells me there are exceptions.