Planted Tank Enthusiast
Join Date: Sep 2010
Location: Southern California (LA)
As far as I know, it's been established that those are flow rates w/o filter media.
Even then, they do give you a ballpark idea. Flow isn't as critical to get exact so there's little need (from our vantage point) for that sort of specificity.
Even visually inspecting your tank for dead spots is enough of an analysis for most tanks.