forgive me if I misunderstood, and don't mean to sound patronizing if you know this already, but first off at present JRiver is not supported with a library installed on a NAS running as the media server (there is a project going on with QNAP, but its not up and running yet I think) -- if you have gotten it to work you have been lucky
Now if this is just semantics and you are meaning that your media files are on the NAS and referring to them as you library that is something else. Also the NAS is running more like a shared external drive rather than a server.
Normally (not always, but ...) you have your NAS with the media files AND one PC running all the time (or preferably "wake-on LANed"). This PC would run Media Server, retaining the library (this is the one you backup and restore) and your other PCs act as clients (which loads the server PC's library - usually on start-up). Every install has its own "local" library (which I find confusing at is always called "Main"), but you would not be using this generally. You can tag/playback/control from any client via the "server" PC (not client to client though), and you are updating/syncing the PC running media server's library. Modifying views on the media server PC will be loaded onto the clients once the are rebooted and the library reloaded.
If however you actually have multiple libraries, on purpose (like you have multiple storage machines) that's something different again, but it sounds like everything is on the one NAS .. so you probably want to /need to consolidate to one if this is the case.
Not wanting to confuse the issue, maybe you can confirm how your network and JRiver are set-up and if by chance you actually have the JRiver library running off the NAS or not and we can take it from there? Otherwise I really can't give you an answer. Probably your library to restore is not where it should be, but I'm not sure
The MC Library to be restored should be the backup off the PC that is running media server, most of the time on an SSD that the OS is installed on.