Nowadays all Search Engines are getting smarter and smarter and their capabilities to collect/crawl billions of websites and store/cache most of the content is bringing up serious issues for webmasters. As you may know Search Engines are not able to store the all the content and therefore they store vector snapshots of non-common/non-repetitive words that have some meaning in order to decrease the storage space and make it easy for analysis and ranking. If you noticed that when you search in Google (for example) and you type in the wild roses are red the search engine marks up only wild roses and red and had neglected “the” and “and”.
When you remove the most-common and junk-words then there are only quite a few words left, and the chances that those word-combinations are not already used by one or few of the billion pages online is quite low and this causes numerous unique content websites to get listed in the supplemental results…….
One of the ways to get your listings up in the regular index and try (at least) to remove the supplemental tag is by adding some more uniqueness into the text. In some cases this can be done by adding some additional text (for example if your title was “web hosting” you can change it to “web hosting by Maiahost” and this would make it stand out from the millions of pages containing the title “web hosting”.
Although adding more text is easier, in most cases this leads to decreased keyword optimization, but considered the fact that being in the supplemental results you practically don‘t rank anywhere, its pretty much ok.
The best way (to my knowledge) is to add more inbound links to your internal pages that are listed as supplemental. This method works quite well but requires a lot of linking to be done, especially if you have a lot of pages that got in the supplemental garbage box. Increasing the Page Priority of each link that is currently in the supplemental pages will most definitely get it listed back in the good priority index.
One of the best affected websites that I got stuck with in the supplemental pages was my directories. In the beginning I had only the title and descriptions, but later on I realized that this ended up directly in the junk index and I had to change everything and pad it with additional string of keywords to both title and description tags. All pages started popping-out from the supplements and now are back in the game.
If you have the same issue, try changing the text, adding some more text and few links.