Google killed the Supplemental Results label from its search results pages. Word of Caution: Just the Label appearing in the result pages, not their Supplemental Index.
What are Supplemental Results?
In 2003 when Google expanded their Indexed pages database, they have created a substitute database for storing less relevant pages called Supplemental Index. Most of the pages went inside this Index were having Lower PageRank or Dynamic/Complex URLs.
When a search didn’t serve enough results from the Main Index, Google check the Supplemental Results and pick some relevant ones from there.
Why they killed Supplemental Results Label?
From 2006 Google has improved upon the Crawling and Indexing support to the web. Even the pages within their Supplemental Index are also started getting crawled more frequent than ever. Remember, previously those pages under Supplemental Index were not getting crawled very often and thus Google considered them with lower priority than their Main Index. After improving the Crawling and Indexing algorithms the Supplemental Index now became Fresh data and more or less at the same level of Main Index.
Does that mean they killed the Supplemental Index?
No, using the search query site:domainname/& you can still see the pages from Supplemental Results.
e.g. site:www.google.com/& – remember that they have killed the Supplemental Results label. So compare the results by removing the ‘&’ from the search query will tell you whether this hack is working still or not.
A Word from the Author:
Evan though they have stopped labeling your Supplemental pages that doesn’t mean you don’t have any. Still you need to work on your Internal Navigation, better crawlablilty and external links to get them out from the supplemental index. Supplemental Results are indication to work more on those pages, instead of complaining to Google, invite them crawl more often by promoting such pages by a better linking strategy. Read more on this at Google Official Blog.