Hello,
Thank you for your message, we are happy to be of assistance.
When performing a regular Google search online, uses their regular free search indexes.
As our system has to perform millions of searches for our clients each day, we cannot use their free search indexes, as they would blacklist our servers for abusing their free system. Therefore we have a business agreement with Google to use their alternative commercial web-indexes which we pay for.
As we previously explained:
The web indexes that Copyscape Premium uses when performing a search are not the same ones that are used when performing astandard Google search. In some instances there may be some differences between these indexes. The indexes we use also getupdated at different intervals to Google's main indexes.
For some reason these two indexes can on some occasions be quite different, so although you may receive some search results using their free indexes, you might not receive any matches when using our system, that in turn uses their commercial web-indexes to search for duplicate content.