A highly experienced organic chemist should be able to deduce how to make it from its structure. It's not like the US government just stumbled upon it, they had chemists that knew about this area and made modifications. Since there are a number of other uses for organophosphates, not all of them classified, there is logically a number of scientists familiar with these compounds, and could make a guess at how to make this particular variation. Furthermore, the reactions to detoxify it are public and in my possession, it stands to reason under the right conditions these steps could be reversed.