I am not sure about the rhetoric: why should you quantify it?
If it is to calculate missed revenue: are you considering that the other side of what I have written - a fact - is that a number of people who downloaded an available copy of your book would not have bought it anyway?
Those relevant to the missed revenue are those who would have paid but did not: the number in that group is something that you can hardly quantify, and on the other hand you have gained buyers that would not have bought your book if they had not tried it.
If it is to calculate missed revenue: are you considering that the other side of what I have written - a fact - is that a number of people who downloaded an available copy of your book would not have bought it anyway?
Those relevant to the missed revenue are those who would have paid but did not: the number in that group is something that you can hardly quantify, and on the other hand you have gained buyers that would not have bought your book if they had not tried it.