The first (?) US 421-A appeared in 1933 along Walker Ave in Greensboro from Market St east to Elm/Ashboro Sts. Walker Ave from Aycock westward was part of US 421 prior to this. In 1937, this was disestablished. Walker Ave is no longer continuous as UNC-Greensboro has gotten in its way. This US 421-A appears only on General Drafting maps from 1933-36. The 1936 Guilford County map does not show it.

US 421-A in Greensboro? 1936 Gen Draft

The 2nd US 421-A appeared in 1952 replacing US 421 through Clinton. US 421-A used Lisbon Ave and McKay Rd.
State officials imply US 421-A was decommissioned in 1957.

US 421 through Clinton 1949 Sampson County

US 421-A through Clinton 1953 Sampson County

The 3rd US 421-A appeared in 1957 or 1958. It began at US 421 (now just NC 18-268) Wilkesboro and headed north on Wilkesboro Blvd and 10th St to N. Wilkesboro, then west on D St out to US 421-NC 16.

No US 421-anything in N. Wilkesboro 1957 Wilkes County

US 421-A appears 1962 Wilkes County

In May 1963 (NCDOT), US 421-A was given one-way splits in North Wilkesboro. NB continued to use 10th St while SB used Forester Ave (now the CBL loop).
In Nov 1969 (NCDOT), US 421-A was dropped from NC 18-268 from Wilkesboro to N. Wilkesboro and renumbered as US 421 Business from N. Wilkesboro west out to US 421-NC 16.

US 421-A on one-way splits 1968 Wilkes County

US 421-A is removed 1972 Wilkes County