The W.R. Case & Sons Cutlery Company has a very rich history that began in 1889 when William Russell (“W.R.”), Jean, John, and Andrew Case began fashioning their knives and selling them along a wagon trail in upstate New York. The company has produced countless treasures and it continues to do so as one of the most collected brands in the world.
First would be--factory error. I think that accounts for most of the knives you see with no tang stamp. However, most show evidence of being sanded/ground off. A few knives I've seen with etched stamps, but Case never used them to my knowledge.
Yes, factory error - you don't see too many of them like that but they do exist.
As to the year, Case first made the 6265 in SS in 1972. The "composition" shield dates the knife to 1974 or later. But it could be any year from 1974 through the early 80's. After about 1984 the shields were changed several times.
Steve Pfeiffer, author of Collecting Case Knives: Identification and Price Guide second edition released November, 2015.