"Another Part Of Me" actually originated from Jackson's theatrical attraction "Captain EO," which played exclusively at Disneyland in California (and later EuroDisney, I believe) for about a year prior to "Bad" being released.
At the time, a soundtrack wasn't available, despite there being three songs in the ~45 minute sci-fi vignette that paid homage to "Star Wars" and raked in significant bucks for Disney for a short while. Interestingly, the other two songs never appeared on an album and "Another Part OF Me," while being included in Jackson's "Bad" LP, didn't even get any remix treatments until three or four(depending on which country you were in) songs off the LP were released as singles before it was.
Still, the song that had been available to the general public one way or another for nearly three years prior to its 'official' release, had enough momentum from the "Bad" album to send it all the way to #2 on the US charts and top ten on the US R&B charts as well. (Of course, by that point if Michael had used footage from the "EO" flick where the song had originated years earlier it might not have fared so well!...)