Correspondence with AASHO is absolutely fascinating...
NC highway Commissioner floated to AASHO in an official memo 12/22/1930 to change US 74 from Asheville to US 17. The number he wanted? US 70-1 which he wanted to go all the way to Wilmington. The response was that AASHO's committee would not approve that.
More fun? There used to be an AASHO rule that you couldn't move a US route from a control point location without providing another US route through the jilted town. Without consulting AASHO, NC moved US 17-1 from Pleasant Hill-Roanoke Rapids-Weldon to a newly concrete road from Pleasant Hill to Weldon directly. They did this by virtue of swapping NC 40 and NC 481 along those pathways and they had previously said US 17-1 will follow NC 40. After AASHO pointed out their error in doing so unilaterally, North Carolina thought the best solution to this was to create US 17-1E and US 17-1W. Can't make this stuff up.