Duplicate entries when importing database from Clementine

[shadowfire]

Re: [Clementine-->Strawberry migration](fixes to SQL)

Thanks, this mostly did the trick. I had to make a minor modification - replace double quotes ("") with single quotes ('') - because it gave me these errors:
no such column: "" - should this be a string literal in single-quotes?

Unfortunately the duplicate songs fix was not persistent; initially things seemed okay but when I selected the 'All tracks' playlist, then 'Smart playlists' -> 'All tracks' -> 'Replace current playlist' my total song count increased. Clementine originally reported 10,061 tracks, (which Strawberry reported the same after the import) but after replacing the tracks count increased to 13.669 tracks.

I can't figure out why some songs are duplicated while others aren't. My mp3s are spread out over several directories (for legacy reasons, I used to divide them up into chunks that could fit on a portable mp3 player or usb stick).
The directory table seems to be the same (without duplicate entries) after import. Also the 'url' field seems to be identically on the duplicates.

II'm scratching my head here, does someone know how Strawberry determine the unique id of a song?