Back in September 2003, the launch of the Supplemental Index led to outcries from the webmaster community because pages included in it were deemed as secondary; thus, leading to the death of their sites’ SEO. This type of index may have been rolled out to allow bots to crawl through and index more pages without users suffering from reduced quality and performance of the search engine. With this November 2006 update, Google rolled out new guidelines that changed how the search engine handled websites that were affected by their filters.
The supplemental index is described as a secondary directory of pages that Google provides to end users in case the query fails to find relevant matches from the primary index. Search terms from this set have the tag “supplemental results” beside the URL in the SERPs.
For some websites, the restrictions implemented in the main index may be ignored for the supplemental index. This freedom allows bots to crawl through sites that may have low trust scores in the main one. However, most pages listed in the secondary directory are often not displayed as results in search queries.
There was confusion on the exact cause of a page’s exclusion from the main index and its fall into the supplemental. It caused outcries of frustration from webmasters whose websites suffered from the loss in rankings. Nonetheless, Google was adamant that the supplemental index was not a horrible place for your site to be in.
Google clarified these three points regarding the supplemental index update
Google had officially scrapped the supplemental results label in July 2007. This move was made to lessen the bias against pages listed in the supplemental index, which were seen as inferior or unimportant to the ones in the main directory.
Since the supplemental index update, the team has revamped the system that crawls and indexes supplemental results. When the label was relinquished, the system at the time conducted more in-depth and more continuous indexing. Now, instead of fixating on whether your pages are in the primary or supplemental index, you should focus on acquiring high-quality backlinks as Google recommended.
Here are the ways to build high-quality backlinks from scratch: