No predictions loaded for 1999. This site serves NOAA predictions from its own store, and this period has not been fetched for Mona 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/pr/mona-island-9759938/1999
Mona Island, PR tide table 1999 (printable) · Tide Almanac