@JohnM Thank you for your help.
I don't know how to answer you though. I suspect the songs aren't displaying simply because they are not in the DB.
I originally imported just over 3000 OpenSong files, there's 1278 records. It would take me a long time to find a song that's there, and not displaying. Unfortunately I don't have the time to do that.
I can though give you the name of a song that's there, but not exporting. For what it's worth.
id=37, "Eternal Father, strong to save"
I suspect part of the issue with exporting may be that songs with duplicate titles are being clobbered on export. I'll upload the first backup I made, so you can see the state of the DB before I started making changes. You'll be able to see for yourself that it's a bit of a mess, with a lot of duplicates (I have no idea why the original OpenSong collection was such a mess).
I'll also include a text file with the titles of the 1003 songs that successfully exported on Kubuntu.