Reddit mentions of Bowes and Church's Food Values of Portions Commonly Used

Good point--in that case I wouldn't doubt for a moment that the numbers for Everclear came from someone doing what I did.

In the spirit of science I dug out my very old Bowes & Church.

1.5 oz 90 proof gin 110
1.5 oz 94 proof spirits 116
1.5 oz 100 proof spirits 124
1.5 oz 80 proof rum 97
1.5 oz 80 proof vodka 97
1.5 oz 86 proof whiskey 105

Now these are generic numbers as you can see, but I guarantee you that some actual scientist tested some actual booze to come up with them. Make of them what you will.