 Originally only one sequel was planned. The script for this sequel,  known as "Paradox" included all the elements of both Parts II and  III, but compressed to fit into one movie. However, it was revealed  with the release of the DVD set that there was an even earlier  script which involved Marty meeting up with his parents while  theyre college students in the sixties. (This was probably dropped  because no matter how you cut it, George and Lorraine wouldnt have  been in college during the "Protest Era", they were too old.)