'Tis exactly as you say LTS.Many a classical composer has used the same process. I was thinking of the likes of Paul Simon who seems to have moments where he genuinely half-believes that he wrote both "Scarborough Fair" & "Silent Night"
Chuck Berry's "My Ding-a-Ling" (Pretty much "Little Brown Jug")
Does anybody know if the Beach Boys ever claimed credit for "Sloop John B"? Works of that ilk.
Any more examples?