I usually report tidal datums and tidal ranges based on the benchmark sheets for a given area. On the benchmark publication MLLW is always Zero.
On NOAA tidal datum reports however MLLW is never Zero. Adding or subtracting the MLLW value from the other ranges gives the correct value for MHHW, MHW, MSL etc.
Why does NOAA report the tidal datums this way where MLLW is not zero? I've seen numerous mistakes made over the years where someone wanted a MHW contour, or they reported the MHW elevation directly from the datum sheet without applying the MLLW correction. Wouldn't it be easier and safer to report tidal datums with MLLW being Zero?
Pick any datum report off this list:
NOAA Datums
Then open the corresponding benchmark publication here:
NOAA Benchmarks
You would have to pick a point in time to establish that datum, and then with sea level rise, those elevations would rise with it..