Herbal resistance true?

Is resistance really ever an issue with herbs? I just don't see why id stop something if they aren't all dead. Wouldn't that in itself promote resistance? Such as, when you take an Antibiotic you are instructed to take the full course and not to stop?

I have been taking my same base formula for about 4 months, but sometimes I add new ones to my regimen on top of it

All the formulas have similar herbs, though

opinions?