Maybe someone has a better source, but look here: https://press.pirelli.com/?h=1&t=Formula%201

They are all the press releases Pirelli had regarding F1. For each race there are the sets available, a preview, and then session by session what drivers used.

In the "Preview they list track characteristics. In "Qualifying", they give possible race strategies with estimates for tire life.

I think maybe there is some way to correlate the track characteristics, estimated tire life (as shown in the "Possible Race Strategies", and compounds to come up with an approximation of a general degradation per compound, though it's worth saying that often the drivers would get more life out of tires than these estimates.

Working from the idea that they had some formula they used to derive these estimates, working backwards from the information they released may give some idea of the formula they used.

Another variable is, of course, that Pirelli gets to inspect the tires after sessions so it's not just based on the equation.