User blog comment:TheHandsomePlant/Zombie Waves - used for future editing/@comment-25154254-20150303132356/@comment-5792287-20150307113533

Yeah, PvZ1 usually randomizes. I've just remembered the other occasions where waves are fixed, most of the time when a new zombie is introduced they're certain to appear in specific waves regardless of how many points that wave can usually spend (for example, first time playing 5-8, you get a Garg right after the first flag).