User blog comment:TVthePunisher/Six Unknown Shinigami/@comment-1405841-20100802221318

You're right, there is no sign of the 10th division...and Kaien (I'm assuming) is kind of cut off on the left there next to Ukitake. Is there any information regarding past members before the current ones? Up until now, I've only heard of 3...

http://bleach.wikia.com/wiki/Tenth_Division

I'd have to review TBTP to be certain if the squad was around during this time, which is speculation to assume that Squad 10 didn't exist during that timeframe. I'm sure there WAS a squad 10, it's just there wasn't a 13th one...then again, it's premature for me to say anything more on the matter before I review the arc. Until then (and when it's stated), it's unknown why the 10th division is not shown.