No predictions loaded for 2021. This site serves NOAA predictions from its own store, and this period has not been fetched for Sumner Island yet. Nothing is estimated or interpolated in its place. NOAA's own page for the station has the official table: tidesandcurrents.noaa.gov.
tidealmanac.site/us/ak/sumner-island-9451163/2021
Sumner Island, AK tide table 2021 (printable) · Tide Almanac