SC 331 ALT: Appeared in Feb 1937 (SCDOT) as new BELT routing from SC 28 (now US 278) along Marion St to Railroad Ave then west to SC 3-331 (now US 278-301) in Allendale.
In Sept 1937 (SCDOT), SC 331 ALT was extended northwest along Railroad Ave to Memorial Ave, which was a different BELT route that was likely either SC 28 ALT or SC 3 ALT.
In 1942, SC 331 ALT became SC 73 ALT. Today it is S-3-10 on Railroad Ave and S-3-14 on Marion St.
SC 73 ALT is explicitly mentioned in SC Highway Department Annual Reports which is why the number SC 331 ALT is known...