User blog comment:Jallu/2 Things!!/@comment-7658432-20130416100911/@comment-1429792-20130417114909

The events of the current flashback happen around 20+ years ago, not 100+ years ago.

Isshin was a captain after the Visored left Soul Society. Hitsugaya only became a Shinigami sometime after Hinamori, who did so about 50 years ago. And Hitsugaya is the third seat in the flashback