Yep that's the knob I was toying with yesterday and going "what the hell is this for?" I do have the owners manual that's posted on the site so hopefully I'll roll around in this over the weekend and see how it does

I think Super-Matic Drive actually came about in 1950 when they offered the HDM and OD as a package. Butler, pp 288-289. Probably that was just a sales gimmick name to sell as a package both OD and HDM. HDM was first marketed in 1942, which was a short year before the war. 1949 was the last year for Vacumotive Drive (clutchless shifting only, equivalent to teh Vac button on HDM). HDM and Super-Matic Drive were discontinued after 1951. The 1952 Hudson options were the GM Hydramatic transmission or the 3-speed manual, with or without OD.

As John said, be happy you have the OD. It's easy to use and very useful to help minimize engine wear at lower speeds.