When the late JC introduced the Castwell knot in these hallowed pages, back in the day, there was much controversy over whether the knot itself was original or some kind of bend knot that had been around for ages. If I remember correctly, JC himself stated that there was no way he invented it, but he had never seen it written up before and knew no name for it.

Let me state clearly, that in my opinion, JC's popularization of the knot makes the attachment of the Castwell name totally appropriate.

That said, this weekend, I came across a depiction of the knot in George Parker Holden's book, Stream Craft, published in 1919. He refers to it as a simple jam knot - with the only difference being that the tag end of the line is tied in an overhand knot to prevent slippage.

I'm not familiar with silk lines or gut leaders so do not know if the overhand knot was necessary.