Published figures for the total area of the deep ocean floor vary by more than 10 percent depending on the depth-contour definition used (commonly 200m) and the underlying bathymetric data set, ranging from roughly 300 to 335 million square kilometers in different sources; NOAA itself states the extent only as a share of the ocean (over 90 percent of the ocean is deep ocean) rather than a single agreed area figure, and less than 0.001 percent of the deep seafloor has ever been directly observed, which is part of why no more precise consensus figure exists.
What would resolve this A single, standardized global bathymetric survey below the 200m contour, using one consistent methodology, of the kind not yet completed as of this writing (Seabed 2030 and similar mapping initiatives are working toward this but are not yet complete).
OpenOceanography and bathymetric mappingHow Much of the Ocean Has Been Explored? (NOAA Ocean Exploration)