Bruno, thanks for the response, miss reading your posts.
The pattern list that you shared with me some time back shows the #21 to be 3.3125" and is described as a Sleeveboard, the #3 is named a Sleeveboard Pen and only 3.25" closed. I'm totally confused, as usual. I'm still hanging on to the name Sleeveboard Pen because both blades are pens and the dimension of 3.25 matches the list. The difference in length, 0.0625" is a lot closer than most carpenters work, maybe not cabinet makers, but reading a tape or ruler is not quite like the answer from a micrometer. That being said I feel like there are knives that are misread, not intentionally but just because it is difficult. This morning I thought both knives were 3 1/4" long but they are not after accurately measuring.
As you said others may differ.
At least I was able to ID the Trapper and the 4" Stockman.