The downloads will only mention the performer, title and album. The only way would the writer be mentioned would in a metedata. Itunes have them. Not sure on Amazon. Also it depends on the release as often you see Trad.

http://www.electricscotland.com/poetry/henderson/singalong/page121.htm for example names it as Kenny MacKenzie

Also it depends on the song. This lyrics isnt readily available online

If it was a popular chances are it may have the writers. Also some songs where the writers are know is used as a trad piece. Ie Ae Fond Kiss