I am a researcher on a J1 visa employed by a US university. The USA has a tax treaty with my country, Romania, based on which I believe my income in the USA is exempt from tax "for a period not exceeding 2 years from the date of his arrival in that other Contracting State" (in the exact words of the treaty).
Six years ago, I visited a different US university for 4 weeks on a B1 visa. It was a short research visit (i.e. I was not employed, but accommodation and a per diem was provided). I hadn't been back to the USA until I got this J1 visa.
Does that previous visit on a B1 visa affect the tax treaty benefits at all? Specifically, what is the interpretation of "from the date of his arrival"? Should it be counted from 6 years ago (meaning that the period of 2 years have long expired), or should it be counted from when I arrived on the J1 visa? Most importantly, I am looking for references clarifying this point.