Google supplemental results comes from a second level index maintained by google. As opposed to the main index, from which the top results of any query comes from, the supplemental results supply the results when the search query returns very few results.
So if your pages end up in the supplemental index, then the chances of their getting top rankings are very slim.
now you may ask, what sort of pages end up in Googles supplemental results, here are a few pointers.
1. Pages with very little text.
2. Pages with spammy meta tags, Title and description.
3. Pages with very few backlinks.
4. Pages with duplicate content.
5. Pages with very long file names with lots of dashes.
How do you get your pages out of the supplimental results?
Get some new incomming links and put some fresh content on your pages.
Try not get into the supplemental results as it is easier to keep out then to get out.
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