Board Thread:Questions and Answers/@comment-27449779-20151222131224/@comment-1210805-20151227105552

All we really know regarding the timeline of these events is that Rukia was adopted into the Kuchiki clan 40 years before the start of the series, while she was still in the academy.

I don't think it was ever stated how much time passed between then and her becoming part of the 13th Division, or how long she was there before Kaien's death.

As for the issue of her recognizing Isshin in the human world, it seems that it's not uncommon for Shinigami to not be aware of what a squad captain looks like. I'm sure we've seen parts with different Shinigami talking about how they've heard that X captain "looks like this". At the start of the series, Renji had to be told who Rangiku's captain was. You'd think that as a lieutenant he would have known this already.