The first US 29-A appeared In 1938 or 1939, when US 29 was rerouted to go directly from Kings Mtn to Gastonia. US 29-A (with US 74-A) followed 29's first routing to Bessemer City before going to Gastonia. By 1939, US 29-A was downgraded to the current routes used today, NC 161 and NC 274.  

The second US 29-A also appeared in 1937 or 1938, when US 29 was given a newly constructed bypass of Kannapolis, Landis, and China Grove. The old route through these places became US 29A. Most people remember a US 29-A here, but the truth is that this US 29-A reverted back to being plain old US 29 in 1940 or 1941, while the 3rd US 29-A was put on the bypass. Today the 2nd US 29-A is not a primary highway, though it does serve as the end of NC 153. The 3rd US 29-A went back to being US 29 between 1947-50 (which it still is) 

The 4th US 29-A appeared in 1940 or 1941 as new construction. This US 29-A served as a direct route from Charlotte to the Kannapolis area while avoiding Harrisburg and Concord. This routing became mainline US 29 between 1947-50.

The 5th US 29-A appeared between 1947-50, utilizing US 29's original routing from Charlotte through Newell, Harrisburg, and Concord. This was multiplexed with NC 49 to Concord and NC 73 back to US 29. This US 29-A was removed between 1953-55, becoming NC 49 and US 601. Today it's still these routes except for right through Newell (used Old Concord Rd) and Concord (used Old Charlotte Hwy).  

The 6th US 29-A is the reincarnation between 1947-50 of the 2nd US 29-A, running through Kannapolis, Landis, and China Grove. This replaced mainline US 29. This US 29-A lasted until the late 1990's (definitely past 1995).
On 9/6/04 Adam Prince reports that the I-85 Overpass still identifies the road as US 29-A.  

The 7thand 8th US 29-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 29-A's were cosigned in their entirety with US 70-A. Both of them were renumbered as US 29 Business about 1960. Today, both of these are unnumbered routes. 

The 9th US 29-A came along in 1955 or 1956 as, US 29 was bypassed as new construction around High Point, Jamestown, and Greensboro. This US 29-A was co-signed with US 70-A for nearly its entire length, except for in High Point and at US 29-A's northernmost mile in Greensboro. US 29-A started out following this route: today's NC 68 towards High Point, then east on English St, then Main St (was multiplexed with US 311) then left town on Montlieu Ave. US 29-A continued northeast to Jamestown (Greensboro Rd and Main St), Sedgefield (High Point Rd) and into Greensboro, where US 29-A used High Point Rd to Lee St (current NC 6) to Fairground Ave, to Aycock St to West Market St. to Greene St (Forbes St. by 1958)., and finally to Summit Ave where it met up with the new US 29 Henry Blvd. north of Greensboro.
Between 1964-68, US 29-A's routing in Greensboro changed to have more multiplex on Lee St NC 6 to connect with Aycock St.
Between 1969-84, US 29-A's routing in High Point changed to eliminate the US 311 multiplex. Instead, US 29-A split into one way streets through central High Point, then used Kivett Dr. to Guyer St to meet back up with Montlieu Av and on to Jamestown.
Also between 1969-84, US 29-A changed its Greensboro routing to include much more of NC 6 all the way to Forbes St.
US 29-A was disestablished as a primary route about 1993. . 

The 10th US 29-A came along in 1957 or 1958,in Reidsville. US 29 was put on a new road circling the west side of town. US 29-A was Scales St and Madison Rd through Reidsville. This US 29-A was renumbered as US 29 Business in 1960. Today it is not numbered as anything.
 

Though there have been 10 US 29-A's, 5 was the most that had been active at any one time in history.