S.D. Codified Laws § 43-28-16
Any instrument affecting real property which was previous to December 31, 1988, copied into the proper book of record kept in the office of any register of deeds shall be deemed to impart after that date, notice of such instrument and its contents to subsequent purchasers and encumbrancers notwithstanding any defect, omission, or informality in the execution of the instrument or in the certificate of acknowledgment thereof, or the absence of such certificate of acknowledgment, or the omission of any notarial or corporate seal from such instrument or the absence of any post office address of any grantee, mortgagee, or assignee of mortgagee, from any instrument, and notwithstanding the fact that the property described in such instrument was not platted as required by chapter 43-21, prior to the recording of such instrument; but nothing herein shall be deemed to affect the rights of purchasers or encumbrancers who became such prior to December 31, 1988.
SDCL 43-28-16