[itsme]

> I don't plan on opening every PDF in the library to check for links to files, as that would significantly slow down the sync
Opening every file is not necessary and not what I asked for.
The feature could be "include all files in the MSP folder into backup and/or synchronisation"
CSV files are one example. They have to be in the same folder as the fakebook file they refer to, but aren't linked to anything.
Another example are files that are the source to generate PDFs in the library. They could be of any type and are not necessarily linked to the PDF. That could be Finale or Sibelius files or whatever.