I have a similar question but with the reverse outcome.
What if I observe maturation increases my Proof? so I have 50 gallons at 110 proof at the date of filling (55 pg)
after maturation I have 48 gallons at 125 proof (60 PG)
How is that recorded for ttb?
If I dilute to 90 proof, I have actually increased my bottle output from the date the cask was filled