Yes, alcohol content is always expressed as a v/v ratio, rather than by weight, and as I mentioned I'm not certain exactly what it means. I think it is the volume of the alcohol, if it were removed to the total volume of the mixture.

Note the way that would work is the v/v fraction of water and alcohol would sum to over 100%. But I'm not exactly sure if that's the way the v/v ratio is define.

I think v/v is just traditional. Proof, at least in the US is defined as twice the v/v percentage. 100 proof = 50% v/v. Proof used to be some more complicated scale, but I forget what it was.

-Richard