Buy a copy of Levine's 'Guide to Knives and Their Values'.
You'll want the 4th edition, since that's the last edition authorized by the author, and has an excellent grading scheme.
The 5th Edition was printed by Krause without his permission and many things were omitted, making it essentially worthless to a collector.
You also need a couple of copies of the reprinted Sears, Roebuck and Montgomery Wards & Co. Mail Order catalogs that show clear prints.
Those are the styles seen during the era - they were what was available on the shelves.
Keep in mind that the collecting of pocket knives has been exceptionally popular for the last 40 years or so - finding good examples isn't going to happen in the junk shops - you'll find the good ones at the estate sales, so doing some actual research will pay off.
Vaya,
Scouts Out!