I wonder how many of these exist - a title track from one album appearing on another. ("Houses of the Holy" was the band's 5th record, but it appeared on "Physical Grafitti", their sixth).
Celtic Frost's "Morbid Tales" did not appear on the original 1984 release of the
Morbid Tales EP (the Noise Records vinyl), although it did appear on the cassette released by Metal Blade Records in the USA that same year. "Morbid Tales" was first available in Europe (Celtic Frost's home) on the 1985
Emperor's Return EP (of course ignoring imports).
Demolition Hammer's "Skull Fracturing Nightmare" did not appear on the
Skull Fracturing Nightmare demo, but would appear on the 1992 LP
Epidemic of Violence.
Helloween's "Keeper of the Seven Keys" does not appear on
Keeper of the Seven Keys, Part I, but that might be cheating (it does appear on
Part II).
Vader's "De Profundis" first appeared on the
Sothis EP, released more than a year prior to
De Profundis, although its just an instrumental.
Out of some 275+ artists in my collection, those are the only examples I could find.