M1 helmet dating
Those with (original) rare or unusual markings or some kind of documented history tend to be more expensive.
Pete Not all liners seem to have gotten a maker's mark.I'm sure a few guys on here can definitely go into more details about WWII liners.When I look for post-war liners (I want the ones that most people toss away ), I look at maker marks, webbing style, front hole or no front hole, tag labels (Micarta style liners), etc.So if you have a liner with one manufacturers logo over the top of another, the logo on top is then the actual manufacturer. The crown stamps are often very small(Firestone, Westinghouse, etc.) or even very lightly imprinted on the inside top of the liner.Use a flashlight to look and clean out dirt that may have accumulated. You could have a foreign version of the M-1 liner or it could even be a newer liner.