tedster - 11:46 pm on Oct 21, 2010 (gmt 0)
When the Supplemental index was easy to explore, it was very clear that a separate record was kept by URL+crawl datestamp. My understanding is that Google keeps all the website data they ever get. They delete user access IP addresses after however many months, but website data lives on and on. You never know what kind of data mining questions might come up in the future, after all.