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They were used to slice a small sample from a cotton bale so that the buyers could ascertain the quality of the batch. I've not been around cotton gins since I was a small child, so I have no idea if this is still done.
There is a purpose to the elongated tang, for lack of a better term, as well. Many of these knives have a long flat section just ahead of the tang and prior to the blade profile itself. The purpose of this section is for rolling some of the cotton with the thumb to find out something about the sample that escapes me.
I have not heard the term ricasso used in respect to folding knives but in a way I can see this use of the term. In the picture below the part right above what is normally called the tang you will notice a flat piece of blade about 1" long that seems to be an extension of the tang prior to the beginning of the blade profile itself. This is where the cotton is rolled between the blade and the thumb. I probably have not explained this well but I think from the picture you can figure out what I am talking about.
An animal would NOT appreciate being spayed by one of those suckers!!
Campbell, that's one premier CS collection!!