It seems to me that a "classic" knife should have been around in "classic times". Of all of the patterns that have been mentioned, so far, only the Barlow goes back to the time "when men were men and sheep were scared".
In its way, the Barlow qualifies as a classic, if only on the basis of nearly every nineteenth century farm boy's having one (or at least, that is the way that it seems, now). Two problems that the
Barlow has in qualifying as an "American classic" are that it is a modification of a British pattern and, fairly or not, farm boys are not always seen as the basis of anything "classic".
The other nineteenth century pattern that may qualify for the honor of "American classic" is the cattle knife. As far as I can tell, this pattern, in its many variations, is a truly "American" pattern that was designed for American conditions. It was also there "to see the Elephant" during the hey-day of the open range cattlemen, a distinction that its post-1890 descendant, the stockman, could not share.
While it is true that the cattle knife has been pretty much displaced by its offspring, especially since World War II, there is still a dedicated remnant of knife users and colllectors who prefer the older pattern. Given the popularity of SAKs and canoes, both having frames that are basically the same as two of the most popular cattle knife patterns, there might even be the basis for a "cattle knife comeback". The rising popularity of Cowboy Action Shooting, and the accompanying obsession on "authentic" cowboy gear, might just help such a "comeback",too.