g1smd - 5:12 pm on Nov 12, 2006 (gmt 0)

>> a page needs to be crawled to get out of the supplemental index <<

It seems to me that most of the stuff that is tagged as Supplemental are URLs that Google actually wants to drop from the index but which they hang on to as Supplemental Results for a year before they are completely dropped. Those include URLs that are now redirects, now 404, or were on a domain that has now expired.

Most of the rest are "live duplicate content" (multipe URLs with same content: one shows as normal, the rest are shown as supplemental) or "historical supplementals" (where the supplemental tag only shows when you search for words that were in the previous version of the page, the same URL shows as a normal result when you search for current content). These don't get dropped from the index until you fix the problem with the site. Until then, random URLs from the site drop in and out of supplemental on a random basis, at random times.