If you already have the files in your library, but cannot play them anylonger, then its likely not related to the network discovery. I would make sure that Windows can actually reach the NAS, only if that is the case then MC can also talk to it.
If the NAS requires SMBv1 to make Shares available to a client, either due to settings or capability, and the library was created before the Windows 10 update to Build 1709, and Auto Import has "Fix Broken Links" set to "No" or "Yes (protect files on missing drives)", then the files will appear in MC but cannot be played. MC will pop up a message saying "File not found" or similar. They will, in fact, have an icon to the left of the record in MC being a red circle with a white horizontal line through it in some MC Views, for example the Artists detail View.
Indeed it needs to be fixed in Windows, and not in MC.
I don't think my NAS was ever visible under JR drives and devices, but it still worked. You need to look in Windows. If Windows cannot see it, JR cannot either. I doubt that JR caused the problem, and JR cannot fix it if Windows cannot see the NAS. If it does not show on your Network in Windows, you must first figure out why - network or permissions issue?
If you resolve it in Windows and you need to assign a Drive letter to the NAS, just make sure it is the same one you were using before. If in doubt, the file path tag for any track in your library will contain that.
I can see my Shares under "Drives & Devices > Explorer > Network > MC Server Name" and open those Shares to see the contents. It is extremely slow to initially populate the view, but it works and once populated is relatively quick.
If AudioVideophile is using a NAS then he could be using URIs (i.e. a Share named \\NAS-Name\Music) rather than mapped drive letters, in which case there is no need to map them now. The file path tag will confirm what was being used before though.
Of course, the NAS could be running a DLNA Server, and that could be how MC found the files. But I hope he isn't doing that, as it isn't an ideal setup.
There are a bunch of discussions on the internet about NAS's not working after the 1709 update. There may be a specific solution for the NAS AudioVideophile has, which doesn't require SMBv1, or if an older NAS it may require SMBv1 to be turned back on again.