I have two sources for Iodine. One is labeled USP, the other, Ricca, states on their label that it is Equivalent to USP with ACS Grade ingredients. Neither the company making the USP or the Ricca Company make use recommendations. Only a doctor may prescribe Iodine therapeutically. I believe the cautions lie with the law rather than an absolute purity distinction. Personally I use both versions in amounts
Dr. Jarvis discusses in his books Folk Medicine and Arthritis and Folk Medicine. If I advertise USP for sale that is what I am selling.If I advertise USP or Equivalent to USP I will sell either USP, or the Ricca_labeled__Equivalent to USP,depending on my inventory at the time. As Far as shelf life, Lugol's is basically inert and
does not go bad. If opened it may tend towards some evaporation but that is about it.
Kept at room temperature, in the amber glass bottle in which it has been shipped, it will last basically forever. My sense of the expiration info is more of a manufacturing demarcation than a statement about spoilage, which doesn't happen.
If it evaporates some, add a little distilled water