The 1942 Draft Registration Card does not ask NOK (next of kin). The question is "name of person who will always know your address", the only other information is occupation, has is self employed, and the back side has physical description.
The WWI cards had 3 differnt types and only one asked for "nearest relative" and the others asked "have you afather, mother, child under 12 or a sister or brother under 12 solely dependant on for support (specify which)?" Robert answered "neither".
In the 1930 census for Nelson County, VA I find a Robert M Robertson age 42 single b. VA parents VA is a farmer with a Benny F. Robertson, widower listed as father in his household.
In 1920 Nelson county, VA I find a Robert Roberton listed as son in the household of Benjamin and wife Sally Robertson.