E.G: Thyme has well known antimicrobial properties and thymol is (or at least was) a component of commercial mouthwash.

Even when we don't make drugs out of the plant itself, it could have been used for the properties we know about today.

E.G: common vervain is known to have diuretic properties, so it's not a long shot to think it has been used for this particular reason at some point. Today we use diuretic to treat heart failure, liver cirrhosis, or hypertension. While they may not have had any way to catalog all this, it seems unlikely nobody ever associated the consumption of a lot of diuretic with people getting better for one reason or another.

People were not dumb, and there were a lot of them, for a long time. They likely tried a lot of combinations of things, on purpose or by accident.

And if you want some anecdata, I've used plenty of preparations from that text for nausea, fever, menstrual cramps (not mine, clearly), poor clotting, sinus congestion, and likely some things that are slipping my mind.

Plants are where we get a lot of medicines from, and while modern pharmaceutical companies may prefer that information not get spread around (it's basically the whole reason we don't have a widespread practice of western medical herbalism in the US), but the fact remains that if you know how to get the medicine out of the plant, it's still totally possible to do so.