Have you check your site lately? Or even wonders why there are some url or link labeled supplemental result? The battle for this this subject was ended by google and rolling out by then according to their webmasterblog. Some excerpts on the post

we are indexing URLs with more parameters and are continuing to place fewer restrictions on the sites we crawl. As a result, Supplemental Results are fresher and more comprehensive than ever. We’re also working towards showing more Supplemental Results by ensuring that every query is able to search the supplemental index, and expect to roll this out over the course of the summer.

The distinction between the main and the supplemental index is therefore continuing to narrow. Given all the progress that we’ve been able to make so far, and thinking ahead to future improvements, we’ve decided to stop labeling these URLs as “Supplemental Results.”

I am not actually understand this move, are they saying they will removed the url that is on supplemental or only the label on google search telling the url as supplemental? On what I read, only the labels saying “Supplemental Results”. And you will not know now that your inner pages or page on your site needs some more tweak in order for it to be rank on their search.

Better yet, one advice though is not creating a duplicate content pages on your sites.