g1smd - 7:46 pm on Sep 27, 2006 (gmt 0)

>> ask the engineer if something as simple as the www versus NON-www issue could put most of your pages in supplemental. <<

We already know that it can and it does.

The Supplemental Index is a repository for several types of URLs.

Firstly it contains URLs that return Duplicate Content compared to other URLs - www vs. non-www, multiple domains, variable dynamic parameters, capitalisation issues (IIS only), http vs. https, etc (with most or all of the duplicates in Supplemental, URL-only, or removed from the index).

Next, it contains URLs that are now redirects or are recently 404, and they hang about in the index for a year.

The Supplemental Index also contains the previous version of the content for normally indexed pages. You see this when the exact same URL can be a normal result for some search queries, and a Supplemental Result for other search queries (Supplemental when you use words that were on the old version of the page and are NOT on the new version of the page - you can see that old content in the snippet, even though it is no longer in the cache or on the real page).