I have never kept any root from one year to the next for selling...
But I do keep root for my own personal consumption.
I just clean and dry them as usual... and once dry I put them in a paper sack right here in my home office and keep them there.
I prep some by slicing up into thin slices, and drying and I just keep them in a glass jar. I consume it a couple of different ways, the dried slices being one. The fine root hair I just eat them as they are after drying... the main body of the root and thicker branches is what I slice.
But then some roots I just keep them whole (neck, root body, branches and find root hair) and dry them good, then just keep them in a paper sack.
When I need them I take out 3-4 and grind them up in my vita mix blender. It turns them into sort of a coarse powder.
I have a tiny bit of ground root left from last years batch of keeper roots now. I should finish it in a day or two. It seems to keep really well once dried in any form, whole root, slices or ground as long as you keep it dry and at room temps (normal room conditions on HVAC system).
You would not want it to get wet or be in a damp place, or too hot... but I expect a cool dry place would be great for longer term storage.
The roots that I dry and keep whole I can't tell any difference in them whether I have had them dried for one month or 12 months. They look exactly the same to me and taste exactly the same too.