Do you know what hydration Robertson really uses?
I covered this topic in a blog post where I stumbled on a "happy accident.. ." http://www.thefreshloaf.com/blog/ironwise
The original Country Loaf is 79% overall hydration.
You mean the way Chad himeslf does it at his bakery, day in, day out? (not what puts in his book for home bakers)
I'm sure it varies slightly day to day on all their breads and I would gander to think its usually a touch higher. Generally speaking in a bakery we have a formula in front of us but its our job to adjust hydration as needed on a mix to mix basis. The ripeness of levain, weather, the flour, are all little variables that change the needed h20. With his newer breads via T3 he does mention that they use higher hydration in the bakery on many of the loaves in the book.
The basic country bread recipe in the book "Tartine Bread" is 77% hydration. As far as the bakery goes, I'm sure it varies depending on the bread, but it seems like it's at least that or higher. Disclaimer: This is only speculation on my part as someone who has eaten more than her fair share of bread from Tartine Bakery and Bar Tartine over the past few years.
In T3 and in some magazine article about Chad, it is reported that he uses hydration percentages from the low to mid 90's. I don't know if it is that high for his country loaf: he uses an 85% extraction white flour now which holds more water than regular white flour.
PS I always make the country loaf from Tartine with 85% hydration (not including poolish). I have a 105% hydration whole wheat in the fridge proofing right now. We'll see how that turns out.