American Bureau of Shipping; they are the classification society doing the in service certification for the non-combatants. I think they just looked at the hull, but not as confident with the components, as some genius decided 15 years ago to mix steel pipe with bronze valves on the sea water system, and weirdly there are corrosion issues. (Funny aside, they tried to pass it over to the normal SWS LCMM 5 years later and basically were told they broke it, they bought it).
NSS applies to anything over 1000 tonnes; anything underneath that for new builds the NSS yards are excluded (which would include Davie if they get brought in officially).