Thank you all for your help.
The only information I have about this knife, which I acquired from a well known firearms historian and museum curator is this: The original owner, now deceased, flew for Air America in Vietnam. The widow could provide no other useful information with regard to when or where he acquired it, or when or where it was parkerized. No assumptions on my part will be made.
One other question: what is the significance/ rarity of the size of the eyelet hole; does this provide any clues?