[Dumyat]

I'm pretty sure I know what the answer is going on this, but will ask anyway.
After adding a new album(s) to my music library, I tend to manually update individual songs I particularly like with a rating and user rating score using metadata editor addon. This is actually a fairly quick process to do just after adding an album to the library and I really like seeing my own ratings in the library views and on the OSD when music is playing.
I had just assumed these ratings were written to both the music DB file and the album NFO file when exporting the library, but this does not seem to be the case after removing, then re-scanning my library today since none of my ratings are now showing. 
Was just wanting confirmation of this and if there is really any merit to manually adding song ratings this way, if they do not actually get written anywhere so that they can be picked up when scanning your library into Kodi from scratch using local NFO data.
Cheers

[DaveBlake]

Song data is not written to album.nfo, only album information goes there.

But the transient song history data - play count, last played and user rating - can be exported to a single xml file and then imported into a new installation or freshly scanned library. It can also be used if you move or rename your music files, the data import cleverly matches library entry to xml entry using a number of pieces of data (not just filename) and will restore playback history and user rating.

If you have a backup copy  of your musicXX.db file then you can point Kodi at it and do the song history export, otherwise I am afraid you do need to re-enter those user ratings this time. But remember to do the right kind of export (to single file, just pick song history as the item to export).

[Dumyat]

If you have a backup copy  of your musicXX.db file then you can point Kodi at it and do the song history export, otherwise I am afraid you do need to re-enter those user ratings this time. But remember to do the right kind of export (to single file, just pick song history as the item to export).

Thanks Dave. Much appreciated.
Yeah, in my haste I believe I made a rather large boo-boo, by not taking a copy of my Music DB File before removing the library and re-scanning right after.
I've just updated a few user ratings on some songs for albums added yesterday and today, then did a single file export as you described and the user ratings were showing under the <song> tag.   
Yup, that's another important lesson learnt, but on a positive note, I've also learnt something new on how to avoid such a thing happening in the future. 
Thanks again....

[HeresJohnny]

transient song history data - play count, last played and user rating - can be exported to a single xml file and then imported into a new installation or freshly scanned library

It would be nice if export to a single file could be optionally automatic via advancedsettings.xml when scanning the library.