Just to revisit this topic, I played in a tournament at Sanford GC about 3 weeks ago. They don't list Ross on the scorecard, but his name is all over the clubhouse and all over their website. They also attribute the clubhouse design to Ross, btw.
Like others, I haven't been able to find Sanford listed anywhere as a Ross design. In all honesty, I didn't see anything on the front 9 that made me feel especially inclined either way. Very pleasant place to play, very reasonably priced, and in very good condition, but nothing about it that screams that it is, or isn't, Ross.
The question was asked earlier in the thread, but you wonder whom else could have been involved. It's just 30 miles from Pinehurst to the Sanford GC, and it was built in 1934 as a New Deal works project. Which sure sounds like a 9 hole Ross routing...
So the bottom line is we'll never know, and Sanford, like lots of other places can claim anything they wish. And they could be right!