Frank Miller's Robocop 2 is actually Robo2 and Robo3 combined, believe it or not. Which in a way, does make more sense than the final products, doesn't it? In Robo2, the cops are on strike while OCP still plots Detroit becoming Delta City and develop Robocop 2; in Robo3, the cops are back on duty and OCP has Rehab doing things that are peaceful only to the public, yet reality they are vicious. In Miller's Robo 2: cops are on strike, and OCP hire mercenaries and later develop Robocop 2 because of their plans regarding Delta City. See? Also, Cain (or Kong in Miller's version) was one of the mercenaries, with Nuke still in the mix; I can't remember since I haven't reads the script in so long.
Also, just to keep it clear, hopefully: Robocop 2 is actually based on Miller's outline of the movie, which was close but different of the final product, and not the script he wanted. Robocop 3, on the other hand, was based on Miller's Robocop 2 script but was heavily rewritten, while his take was rejected completely (explains his POV of Hollywood which is why he wanted control when it came to Sin City) and unseen until the latest Robocop comic: Last Stand. Also, he was the one who created the gun arm for Robocop 2, but was deleted until he was used in Robocop 3.