S.C. Code § 12-16-740
If, after the filing of a duplicate federal generation-skipping tax return, the Internal Revenue Service increases or decreases the amount of the federal generation-skipping transfer tax, an amended return must be filed with the department showing all changes made in the original return and the amount of increase or decrease in the federal generation-skipping transfer tax.
If, based upon the deficiency and the ground therefor, it appears that the amount of tax previously paid this State is less than the amount of tax owing, the difference together with interest, as computed under Section 12-54-25, must be paid upon notice and demand by the department. If the person required to file a return and pay the tax fails to file the return required by this section, any additional tax which is owing may be assessed, or a proceeding in court for the tax may be begun without assessment, at any time prior to the filing of the return or within thirty days after the delinquent filing of the return.
S.C. Code § 12-16-740