[stcredzero]

How could they even reasonably measure the market value of his skills changing so much so quickly?

Let the market do it. When someone comes with an offer, give a counteroffer and convince them to stay.

There's no way they can justify giving a person who's been with the company for 10 years 4x salary growth in 2 years.

Why not? Markets are better at pricing things than bureaucracies.