It's possible that Bucks could have made it into westerns. Most movies, especially back when westerns were really big, weren't too concerned with such minutiae. The Wild Bunch, for example, has numerous firearm related idiosyncrasies. They probably figured, "What kind of nerd is gonna fact check whether the character could have had a Buck knife or a Barlow", and so on. They never dreamed of an audience with so much free time on their hands, and an internet database to disassemble their movies shot by shot.
One thing that is interesting about that shot is that O'Brien flicks the blade open as if it were a modern one hand opener with a thumb stud.