As described by Neobeo, JJ2/JCS allow thirty-two bytes for each event, but only the first eight of those describe the Event ID. If JJ2 was rewritten to, say, get rid of Illuminate Surroundings, we could have 512 unique events. As it is, there are only 256 events possible, and while it's slightly more complicated than that when different events share the same id, there's no possibility of finding an unknown #666.