We've discovered a strange trend in the bodies of the early zombies. The older zombies have large circular marks on their skin. At first they seemed like normal cuts or scrapes from the environment or run ins with other people. But then we continued to notice them only on the early zombies. We have a very non-scientific process for grouping them. Usually simply new and old. Occasionally we'll pull out some pop reference to a type of zombie based on its movement style, but really it's really about whether they are fresh or not.
Suzanne and Cory were the first to put together the connection to the age and marks. Fisherman refer to them as sucker scars. We then recounted the earliest stories of zombies being found in coastal areas. If memory serves, the Pacific Northwest was the first hit. Canada might be able to claim the title but their news is so far less sensationalized that the U.S. stole all of the early attention.