Would someone explain the different 6.5 branches?

[kirstein]

I haven't found answers to this in a search, but if there is a post explaining this please point me in the right direction.

There are three current branches of WM that I know of.
The first is the 21xxx branch, which I assume is windows 6.5

Then there is the 23xxx and 28xxx branch. I assume these are both 6.5.x versions, is one 6.5.3 and one is 6.5.5? Do both have the taskbar at the bottom? What are the differences between the two?

I've read they are different development teams at Microsoft for these branches ....is that right?

Any insight would be appreciated.