Hiroaki Izumi wrote:
Or is 2-kyou an extension of 6-kyou?
Well, it wasn't for Morihei and Kisshomaru Ueshiba when the book Aikido
was first published in 1957. There 1, 2, 3 and 4-kyou are all described. There is no mention of 5-kyou or 6-kyou. So, if they were practised at all--and there is evidence from the 1938 Budo
volume that 5-kyou was practised, they were not considered to be core kihon waza.