g1smd - 3:28 pm on Sep 7, 2008 (gmt 0)

Google used to reindex their Supplemental database several times per year. At that time I would see a lot of changes. The fresh tags and Supplemental tags, as well as the cache date, were key to spotting what was going on - and Google has now hidden most of that data.

At the moment I don't have any sites that I could track to look for that same pattern. However, in any case, the Supplemental refresh is supposed to be a much more frequent and ongoing thing if I correctly understood what Matt Cutts said about that topic some time about a year or so ago.