Pretty much my understanding too. Muskrat trappers tend to run some large traplines that weren't as spread out as lines for larger, more diverse furbearers, or did at one time. "Rat" trapping tends to be a bit more of a volume operation than some other types of trapping. A rat trapper may have traps covering several ponds and creeks on a number of properties, but in an area more easily covered than say a bush country trapline in Alaksa or Canada. If he's lucky a trapper will have a large number of "rats" to skin out and need to do it quickly. The thin clip blades are excellent for that purpose. Since he may have a large number to skin in a short time, it's good to have a duplicate blade so, as Bartelby pointed out, as the first quits cutting smoothly you can just close the first and open the second blade and keep skinning. Then after the skins are fleshed, stretched, and hung you can sharpen both blades up for the next day.
Naturally, this works for skinning a number of small game and even fish.
The Muskrat is truely a specialized pattern, or as I like to call these and other specific use patterns, purposeful. Harness Jacks are another knife that strikes me as purposeful.
