User blog comment:Willbachbakal/Co-Op Enemies: Security Bot/@comment-1999649-20120412003200/@comment-1330314-20120412005815

Each Bot would spawn with only one mutation, otherwise you'd get huge difficulty spikes. Also, I may not have described the mutations as clearly as I would've wanted: each tier of mutations simply indicates the point in the game where they unlock. Every one of those mutations can appear on any Bot, regardless of their type and upgrade path.