POPULAR HERBS ideally are purchased from the commercial sources before the next season. Out of country commercial herbs supplies the world----impossible to know how old they may be; they would want them to be fresh each year, but impossible to know=.
THE ONLY WAY you know for sure is to grow your own or wild harvest what you can find.
maybe 40 years ago there were well known American family herb sources, but as they grew, they started importing---there are still people on ebay and various places that will still go out and harvest various herbs and then try to sale.
i Guess it all depends on what herb your looking for and a good commercial source you can ask how old it is----they know when they had to last order it, etc. NO COMMERCIAL source deals with less than a pound and no discounts unless you buy X amount and most do not give free shipping unless your spending several hundred $$$.
To wild craft herbs is not hard---but drying them and then collecting a full pound dried---that takes time and effort and then to package and ship normally suggest the shipping people make the most $$, that and most states probably have laws against it---they literally have endless plant laws that they never enforce, but created if they wanted to some day----such as: "IF" on your property you do not put a fence or border around the weeds you want to harvest---those weeds do not belong to you--they belong to the state---the same as the land belongs t the state and you the human is owned by the state. Each state has hundreds if not thousands of bazaar and beyond crazy laws created over the past 200 years by people that must have been insane (greedy).
ONCE a plant / fruit / vegetable has been picked----the life leaves within 7 minutes. Only the seeds then have life and bacteria starts to do its work immediately. So most people only eat dead foods--unless they directly pick from the tree, bush or vine and eat on the spot.
Herbs are dead and like dead foods---all they can do is supply the blood stream with usable organic minerals----naturally bad foods, bad herbs supply the body with something it has to get rid of.
If you search the internet for fresh herbs, you should find sources. I noticed years ago for some of the really hard to find herbs---there are herb buyers listed, but they only buy and will not sale---so they are probably purchasing for some large company out of country, etc. Such as Virginia snake root, for 20 years I can find buyers, but never a seller.
I like to pick herbs fresh and turn them into liquids the same hour---then those liquids will in theory get better with age---ideal at 12 years old and even better when 100 years old.
With Tea cut and powders you have to find the commercial supplier you trust best....some will sell to the public, many sale only wholesale to re-sellers. It just depends what your looking for and how much your looking for.