Yes. In order to provide you with the most complete results possible, Compilatio follows a complex process for searching sources.
In addition to its own databases, Compilatio queries different search tools and centralises the results obtained. To find a source, Compilatio uses the same path used by the writer of the analysed document. If the writer knew how to find the document, Compilatio can also find it.
The search for similarities is carried out on the entirety of the freely accessible web (without needing to sign in).