George, I don't believe there ever was a #1 either (just like there never was a #99 as in Monon Bell lore).
The history of the SW1's is rather strange, too. Though #DS-50 was indeed MONON's first diesel, by 1947 it had been apparently been deemed unsuitable (while stationed at Monon?) and so was traded in during the purchase of the second batch of NW2's. But then just two years later, in 1949, MONON purchased two new SW1's, #'s 5 and 6, stationing them at Bedford and New Albany. They were also seen at Indy's Belt Junction later. Go figure.
I sure would love to see documentation on how these kind of decisions were made and why. Never seen such a thng, though.