My understanding of this Excess CAPE is that it measures by how much the earnings yield exceeds the return on 10 year bonds over inflation.
Earnings yield 3%, 10 year bonds yield 1%, Inflation 2%. So the Excess CAPE is 3 - (1% - 2%) i.e. 4%. Numbers roughly current just to create an example.
The actual Excess CAPE at present is about 3%, from the 3rd link above
I understand this to mean that while stocks are expensive, they are not very expensive given that interest rates are so low.
It seems to me that there is nothing in this that Benjamin Graham would not recognise, except rather than talk about the Excess CAPE he would say the discount rate is low and this supports high valuations for stocks.
I think he might go on to wonder what will happen if (when) the discount rate were to rise.
Actually that is mathematically an easy question.
Let us assume that the correct discount rate at present is 2% and a given stock is priced at €100. All else being equal if the discount rate rises to 3% that stock will fall to €66.66