rokkyo and nanakyo are now classified in Iwama as Osae waza
Interesting. I've read that various arts based the concept of a gokyo on five element theory. Daito-ryu, yamate-ryu, and judo all have a curriculum of techniques they call a gokyo. The difference in Aikido is that we use the term to refer to a specific technique. 5 elements, 5 teachings, each with a feel connected to an element. That's why I've always looked at the idea of "rokkyo" as a little misguided. But perhaps I've missed something.
Oh, and if yonkyo doesn't work, you've done it wrong. Probably because you (not necessarily you particularly Nick, I'm speaking in the general sense) were trying to make a pressure point hurt rather than using the wrist to control the body. The technical name for it tekubi osae - wrist pin, not pressure point attack.
Enough outta me.