I have some questions about the structure of the Cookies directory

Factual Questions
1

A) I’m puzzled by entries such as these:
…@amazon[1].txt 4/26/2005
…@amazon[2].txt 3/24/2005
…@amazon[3].txt 1/06/2007
…@amazon[4].txt 9/12/2006
…@amazon[5].txt 10/20/2006

Are they all active, or only the one with the highest number? Or the newest?
Why are they not named in date order?
If I delete the latest one will I revert to my prior settings or will I lose all my settings?

B) What is the role of index.dat?

2

Sometimes I screw up my defaults for a site and want to go back to an old cookie.
I can’t figure out how to activate it by itself, end up restoring the whole cookie folder, setting a lot of other cookies back.

Any way to just reactivate one old cookie?