[Zubersoft]

How are you going about adding your books of songs? MobileSheetsPro requires unique filenames so long as it is the one managing your files and folders. Is each book just a single PDF or do you have many PDFs? Do the same PDFs show up in multiple books, or are you just running into issues with the files being named the same thing as other files already in the library? If you want to manage your own files and folders, you can uncheck Settings->Storage->Let MobileSheets Manage my Files before importing, and then you will just need to manage your files yourself. 

Mike