Since you can't really skip primary objectives like you do in TW, the rule should probably just be not completing any secondary objectives. Not completing certain secondary objectives in certain missions can increase the difficulty somehow. For example, in Persuade Him and Tacitus Regained, not completing any secondary objectives makes you face more enemy reinforcements.

Like the Juggernauts who invade your base if you don't take out the tunnel network? Yeah I agree, a category for that would be good. But not a lot of people seem to run the later C&C games. Would anyone notice or even contribute?