Here’s a brief look at some major issues with duplicate content over the years… The SupplementalIndex. In the early days of Google, just indexing the web was a massive computational challenge. Practically, the pages you want indexed may not get crawled.
In principle, the further down a navigational hierarchy a page is, the less authority it receives from the page above. For a long time, this threshold was called the supplementalindex , although I’ve not heard that term mentioned for quite a while.