Buck didn't 'invent' anything. They just did a heck of an advertising campaign and dressed it up with big brass bolsters that weighted a ton. The old German Mercator k55 was a rocker type lock back. So were the old Puma stag handle folding hunter, the lock back German F. Herders, and the other stag handle German folding hunters I saw in my younger days long before the Buck 110 was around. It's just like automobile were around before Henry Ford came out with the model T.
Hmm....
I can see the similarity to the K55.
I'm sure I put this question off on the wrong foot by using the undefined term "lockback". I should have asked, what was the first incarnation of the "Buck-style lockback". While the Mercator design uses a pivoting rocker bar like the Buck there are some significant differences. a) The Buck style rocker bar is full length. The Mercator is very short. b) The rocker bar release is in the butt end of the frame, eliminating the problem of accidental disengagement. The Mercator style lock is exposed. c) The Buck style uses a simple, easy to mass produce piano-wire style spring.
I think you are absolutely correct that the Buck design is evolutionary, not revolutionary as it obviously builds on and extends earlier designs. In this way, I think you and Mr. Levine are both right. Buck didn't invent the lockback out of the blue, they just extended prior designs. But at the same time, the combination of design features that Buck brought together appears, to Mr. Levine's studied opinion, to be a first. I mean, of all people in the world, Levine is very aware of the Mercator design when he credits the Buck 110 as a first of sorts.
I think lists such as the one in this thread are interesting in terms of what gets added and what gets left off (to be brief). The Buck-style lockback has become a standard in the industry, not the Mercator style. This is why when we talk about a Case or GEC
lockback, we mean a knife that uses the same design as the Buck 110. For this reason, I think the emergence of this style of lock should be on the short list along with the slip joint, liner lock and frame lock designs.
I would love to hear more about the Pumas and other German locking knives you referred to. Again, I would think Levine is/was aware of them when he wrote what he wrote about the Buck lockback. I'm guess there are some differences in the design? Pictures?