Sorry, I misinterpreted the intent behind your previous post.
As for your question (in blue)...
Let us imagine that we measure with two flash units of exactly equal power but tested in two places...1/3 difference amounts to perhaps f/14 on the minus side or f/17.6 on the plus side.
So, due to lack of standardization of testing, Test A comes out with GN140 while Test B comes out with GN176. As a result, if a reader of the chart is trying to 'overpower the sun' (as so many want to do during outdoor portraiture), shooting at ISO 100 from 10' away, the reader is led to believe that one is too weak to even equal the sun while the other exceeds it by a small amount, so they choose the unit tested in Test B
...yet the one at Test A has the exact same amount of power as the one in Test B! Misleading result of testing in two locations, two identical-powered flash units!
I don't know if you shoot outside in the sun but all I would say when shooting outside and trying to match/beat ambient, 1/3 difference with a typical 500-600ws doesn't make much difference. Yes I am over simplifying things but sometimes that is what you need. Any ways, I will let you guys carry on.