Your herbal wild herbs business is an amazing thing by the …

Your herbal wild herbs business is an amazing thing by the way. Meaningful stuff. And your experience, with the mullein especially, sounds great. I'd like to try that as well myself.
As to why some people can eat crap and be fine, that's a topic full of toppics we can say.
Some just burn everything and expell the rest like as if they were some machine. Some eventually get terribly ill as if out of nowhere. But over all, the reasons why, come with a load of other things that one could get into dismantling for hours.