Possibility to validate if specific documents are within the Doc Lib

I have some specific requirements for a Document Management System. A client of mine has for each customer a Site Collection. In the RootWeb has set some values regarding the type of customer. Based on those values there must be uploaded some specific documents.

But how can you validate if the documents are in the Doc Lib. I would like to have some ideas from the community, because I cannot think of the best way.

Thanks