Re: ikkyo vs ikkajo
I studied daito under three different teachers, None for more than two years at a stay. What I say in the following could be quite wrong. It comes from the accumilative memory of these experiences.
Ikajo, Nikajo, Sankajo, Yonkajo, Gokajo all refer to techniques originally designed to defeat grabs against one's jo staff.
Translated to empty hand combatives, one's forearm can relax (with form) and the bone of the forearm acts with the same leverage of the lifeless wood (the Jo). Of course, Ikkyo is performed in the same way and Ron's history of the terms stands firm.