There are 6 herbs with 3 ranks each. So that is 18 quests you cannot redo. That's what you get back from the books.
As an example of a crafting. If I have level 700 tailoring, with all the crap from years ago.
I do my 30 odd quests and get rank 1 of a load of new crap.
If I drop that tailoring to get enchanting and de crap. I can book back Tailoring and I will get all those rank 1 recipes back and only those.