In late 1934, US 521 dropped its state route multiplex with NC 26.  

In 1969, US 521 was extended north along South St, then west along the Billy Graham Pkwy to end at I-85. Sadly, this was 521's farthest reach at 19 miles.  

In the vicinity of 1996, US 521 changed its route to multiplex with I-485 from Exit 65 to Exit 61, then proceed south along new construction to South Carolina where it met back up with Lancaster Hwy right around the state line. Lancaster Hwy from Exit 65 southward to the Palmetto State became unnumbered. 

In 2003,, AASHTO approved US 521 north to be truncated to its current end at I-485 Exit 61. Everything north of Exit 65 is now unnumbered as primary routing, but the Billy Graham Parkway is still signed as Charlotte 4.

US 521 is now North Carolina's shortest U.S. Route, but it is also the only U.S. Route in N.C. to be 100% 4-lane. Like that was hard.
Adam Froehlig reported in September 2004 US 521 was still posted from I-85 at the Billy Graham Pkwy exit, even though the 2004 Official Map shows the truncated routing of US 521 .