US 276 Bus #1: Appeared about 1947 when US 276 was placed on Stone Ave around central Greenville.
In 1970, US 276 Bus was renumbered as I-385 Bus on North St; unnumbered between Church and Main (now SC 183); renumbered as US 25 Bus on Buncombe and Rutherford (now SC 183 and S-23-200).
Strongly implied on officials 1947-69 and explicitly shown on topo maps.

US 276 Bypass explicitly shown 1966 Official

US 276 Business through Downtown Greenville 1958 Topo

US 276 Bus #2: Existed only Oct 1983 to May 1984 (per AASHTO minutes) when at least on paper, US 276 was moved to the newly constructed I-385 between Mauldin and I-85, then on around with existing I-385 back to Stone Ave. US 276 Business was assigned to mainline US 276 through Mauldin into Greenville. In May 1984, US 276 Business went back to being mainline US 276 when I-385 was extended to I-26. I doubt this existed long enough to be posted.