No predictions loaded for 2018. This site serves NOAA predictions from its own store, and this period has not been fetched for Shag Rock 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/shag-rock-9454125/2018
Shag Rock, AK tide table 2018 (printable) · Tide Almanac