Other than "I'm reading the specification incorrectly", I don't understand but take your experienced word! 
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basically he's saying that 6b/gram is the lowest cell count you can expect to encounter within the best by window.
What the specification sheet from Fermentis says is- in a typical analysis you will see greater than 6 billion cells per gram
at packaging. This is different from the number of cells you can expect to get, as that number will depend on a number of factors- such as storage and rehydration.
I have pitched 1 and 2 packs of US-05 into 1.060 worts and liked the results of both, no real distinction between the two. I have also pitched 1 rehydrated and one straight into equal worts and noticed no ascertainable difference in the resulting beers.
What my experience has shown me is that there is a very wide range of "pitching rates" which will make very good beer. Chasing down a specific number that is in the billions is futile. Consistency with your processes is far more important to me. You have to decide for yourself what you like.