For example, today, while listening to some Ennio Morricone soundtracks, I made a very interesting discovery. I've never seen the 1967 spy film MATCHLESS, but while listening to an mp3 of the soundtrack album, I quickly recognized elements of the first track -- "Donna e amori" -- as coming from Mario Bava's film PLANET OF THE VAMPIRES. This film, scored by Gino Marinuzzi, Jr., was produced two years earlier than MATCHLESS. The sounds heard during the first 18 seconds of the cue -- the low bubbling sound, the intermittent foghorn-like bellowing -- just prior to the ascending, layered brass pattern, are heard in PLANET OF THE VAMPIRES during the opening scene aboard the spaceship Argos and probably elsewhere, as well. Then, from 00:49 - 00:53, just after a brief electric bass solo, the track utilizes another sound heard throughout PLANET, even under its opening titles: a kind of sparkling electronic chatter, which later repetitions of the sound in a lower octave (for example, 1:45-49) reveal as electronic keyboard vamping, probably by Bruno Nicolai, who played something vaguely similar during the animated IdentiKit sequence of 1968's DANGER: DIABOLIK.
This discovery raises some interesting questions. Could the components heard in PLANET OF THE VAMPIRES actually be the uncredited work of Ennio Morricone and Bruno Nicolai? If so, even if these were library tracks at the time, it would allow us to add another Morricone collaboration, or at least an asterisk, to Bava's filmography -- which presently allows for only a single such collaboration, the justly-celebrated DANGER: DIABOLIK. (I'd have to listen to the PLANET soundtrack CD again to make sure, but I don't remember these bits being present on the Digitmovies CD, which would suggest that they weren't Marinuzzi's work and did originate from a film music library.) Another possibility is that Morricone sampled these sounds by Marinuzzi, who was in fact an accomplished electronic composer; this possibility holds potential too because the MATCHLESS soundtrack ends with a reprise of "Donna e amori" that completely omits the electronic musical effects to which I'm referring and sounds much the more organic of the two versions.
If any Morricone experts out there are able to shed light on the questions raised by this discovery, please let me know.