Mean of the high water springs only excludes a handful of tides every year, so generally it’s very safe to place the coastline at least as high as water visible in imagery. If you are unlucky enough that the imagery was captured in the few hours of the year the tide goes over, it’s generally just a foot or so most places. Hardly noticable given the often much lower precision of coastline in OSM.
Coastline in OpenStreetMap is more often too low than too high, if one looks at the actual definition