Board Thread:Questions and Answers/@comment-1754938-20150922055002/@comment-26269901-20150922113531

Kishen1912 wrote: Of course Kaien would have been unknown. She was graduated and fast tracked into squad 13 immediately after induction into the Kuchiki house.

But its hard to imagine that 20 + years in squad 13 and she never saw captain of squad 10 ! That is what I am saying ! I don't know if it was said how long Isshin was captain of 10th division, but I recall in Turn Back The Pendulum it was talked about how captains change often, so it's possible he wasn't on that position long. Rukia was also known as someone who didn't socialize much, until she met Ichigo and his friends. It's quite possible they simply missed any chances of meeting.

Or we can simply chalk it up to Kubo accidentally making a plot hole.