S.C. Code § 12-39-220
If the county assessor shall at any time discover that any real estate or new structure, addition, or improvement duly returned and appraised for taxation, has been omitted from the duplicate, he shall immediately appraise it and notify the auditor. Upon receiving notification from the assessor, the auditor shall charge it on the duplicate with the taxes of the current year and the simple taxes of each preceding year it may have escaped taxation subject to the limitations contained in this section. And if the owner of any real estate or new structure, addition, or improvement thereon, subject to taxation, has not returned or reported it for taxation, according to the requirements of this chapter, and it has not been appraised for taxation, the assessor shall, upon discovery thereof, appraise it and, upon notification from the assessor, the auditor shall charge it upon the duplicate, with the taxes of the then current year and the taxes of each preceding year it may have escaped taxation, and all applicable penalties upon such taxes of preceding years subject to the limitations contained in this section. The adjustments determined by the assessor may not extend back more than three prior years from the year the adjustments are determined but in no event back to a prior year before the year the addition on improvement was made. The term "improvement" for purposes of this section means a change to any real estate or structure which betters the value thereof while not constituting regular maintenance.
S.C. Code § 12-39-220