[BRX]

I must be missing something. I thought each library was totally isolated, no interaction at all, backup separately, sync separately, etc. Unless each library was active on separate devices, which doesn't make sense to me.

The libraries use the same files if you don't set it up differently. I see that as a strength and not a weakness since it saves space and you *can* change songs globally if you edit them externally (or with the feature within MS to save tp the PDF).

Now, annotations and such are saved to the library and don't affect the source song unless they are intentionally saved to PDF. 

IMO it's up to the user to be aware that if he changes a source PDF externally or writing to it it affects all the songs that are referenced in the database(s) regardless if they are in multiple collections, albums or libraries. If he wants tö edit externally (which shouldn't be often IMO) than I see it as obligation of the user to set up different locations/files/names for the PDFs so only they are affected. I really dislike to have identical duplicates on a tablet (or in general) if it really isn't necessary (I dislike the iOS file restrictions as well).