The first US 70-A appeared In 1937, as a total renumbering of the original NC 9. Ran from Durham to Raleigh, starting at Downtown Durham and heading east on Holloway to Miami Blvd. and proceeding southeast to Raleigh along Glenwood Ave to W. Peace St, then east to Wilmington St, then south to Morgan St, west to Fayetteville St., then south to Lenoir, where it met back up with US 70. Between 1948-50, this US 70-A became mainline US 70, which it largely remains today, save a few changes in Downtown Raleigh. The last few miles of US 70-A were multiplexed with US 15-A.  

The 2nd US 70-A appeared between 1943-46, when a new road bypassing Hillsborough was built on the north side. US 70-A was put on this road. This was renumbered as mainline US 70 by 1952.  

The 3rd US 70-A appeared about 1946, when US 70 was given a newly constructed bypass of Hickory. The old route through these places became US 70-A. This route was denumbered totally in 1957 or 1958. Today it is just 1st Ave and Highland Ave. This US 70-A had been part of the original NC 10.  

The 4th US 70-A appeared between 1948-50, when US 70 was given the more direct route between Durham and Raleigh. The old route of US 70 through Cary became US 70-A. This route left Durham via Angier Ave. From there US 70-A went to Bethesda, where it veered due south on today's Miami Rd until it reached today's NC 54 at Nelson. US 70-A followed today's NC 54 to Cary, then used Chatham Rd and Hillsborough St to continue towards Raleigh. US 70-A entered Raleigh using Western Blvd to Boylan Dr, then South St east to Fayetteville St.
In 1951 or 1952, US 70-A was extended on the west end, along Pettigrew St to Chpael Hill Rd to Duke St to Main St to 9th St, to Hillsborough Rd west out to the new US 70 Bypass about where I-85 and NC 147 meet today. This extension replaced mainline US 70.
In 1957 or 1958, this US 70-A was reduced to just being the business route through Durham. Durham-Cary-Raleigh was denumbered from Downtown Durham to Nelson, but Nelson to Cary and Raleigh became part of NC 54. Much of the Cary to Raleigh part is unnumbered today. As a part of this change, US 70-A was extended east from Downtown Durham via Holloway St out to Miami Blvd. then southeast to the new US 70 Bypass.
This US 70-A was renumbered as US 70 Business in 1960. Most of this is still US 70 Business today.  

The 5thand 6th US 70-A's appeared in 1951-52, as the routes through Lexington (Ran along Main St all the way through Lexington) and Thomasville (It used Main St and Turner Rd. to run from Pilot, to central Thomasville, then back to the current NC 68 south end). Both of these US 70-A's were cosigned in their entirety with US 29-A. Both of them were renumbered as US 70 Business about 1960. Today, both of these are unnumbered routes. 

The 7th US 70-A appeared in 1951 or 1952, as the route through Hillsborough, using W Hill and King Streets . This US 70-A was renumbered as US 70 Business about 1960, as it remains today. 

The 8th US 70-A's appeared in 1953 or 1954, as the route through Morganton (Ran along Union St all the way through Lexington). This US 70-A was renumbered as US 70 Business about 1960, as it remains today. 

The 10th US 70-A came along in 1955 or 1956 as, US 70 was bypassed as new construction around High Point, Jamestown, and Greensboro. US 70-A started out following this route: today's NC 68 English St towards High Point, then north on Westchester Dr, then East Lexingtom Av. US 70-A continued northeast to Jamestown (Greensboro Rd and Main St), Sedgefield (High Point Rd) and into Greensboro, where US 70-A used High Point Rd to Lee St (current NC 6) to Fairground Ave, to Aycock St to West Market St. and proceeded on Market to exit Greensboro to the east. US 70-A continued to Burlington and Haw River, and finally met back up with US 70 at today's I-85 Exit 161 connecto west of Hillsborough. In all cases this route had been mainline US 70.
In 1962 or 1963, US 70-A east was truncated to Henry Blvd (US 29-70 freeway) on the east side of Greensboro. The rest of US 70-A over to Hillsborough went back to being mainline US 70.
Between 1964-68, US 70-A's routing in Greensboro changed to have more multiplex on Lee St NC 6 to connect with Aycock St.
Also between 1969-84, US 70-A changed its Greensboro routing to include much more of NC 6 all the way to Forbes St.
US 70-A was disestablished as a primary route in 1993.  

The 11th US 70-A came along in 1957 or 1958, in Goldsboro. US 70 was put on a new road bypassing the north side of town. US 70-A was W. Grantham to N. George south to Ash St and eastward out of town. This US 70-A was renumbered as US 70 Business in 1960, which it remains today.  

The 12th US 70-A came along in 1957 or 1958, in Kinston. US 70 was put on a new road bypassing the south side of town. US 70-A was Vernon Ave to Queen St south over the Neuse River out of town. This US 70-A was renumbered as US 70 Business in 1960, which it remains today.
 

Though there have been 11 US 70-A's, 5 was the most that had been active at any one time in history.