You’re assuming that there’s a small number of herbs discovered a limited number of times and spread over a large geographic region, as opposed to a large varie

You’re assuming that there’s a small number of herbs discovered a limited number of times and spread over a large geographic region, as opposed to a large variety of potentially beneficial plants discovered multiple times independently by people who spent literally their entire lives, for generations, interacting with their surroundings. Yes, if someone discovered aspirin, and you want to know if it ever reached another continent, your model is useful; if your question is generally “did humans intentionally consume bioactive plants with knowledge of their effects”, I can pretty confidently say the answer is “yes” for any group of humans who spent even a generation living in the same place. Again, these folks lived primarily forager lifestyle, in which they had to know which plants they could eat or they would literally starve to death. They knew their environment.