"In January 2024, we acquired the remaining noncontrolling interests in Pilot for $2.6 billion, increasing our ownership of Pilot to 100%."

So, the second tranche implied a total value of $19.8 bn (41.4% for $8.2) but the final tranche for 20.0% implied a total value of $13 bn.
The negotiations for the exact number for the final tranche may have included an implicit credit for the high second tranche, so the "value" may be higher than 13, but presumably under 20.

Ok, good point, I had missed that $2.6b number for Tranche 3. (I saw a January article where it said the amount was undisclosed, but as you point out Berkshire subsequently disclosed it in the Q1 report.)

So we have:

Tranche 1: 38.6% for $2.8b, i.e. implied total value $7.3b (in October 2017)
Tranche 2: 41.4% for $8.2b, i.e. implied total value $19.8b (in January 2023)
Tranche 3: remaining 20% for $2.6b, i.e. implied total value $13b (in January 2024).

Tranche 3 may indeed include some adjustment for the overpayment in Tranche 2, given the favourable legal position Berkshire presumably found itself in, with what seems like clear evidence of fraudulent behaviour in Tranche 2, so one might conclude that the implied total value was higher than $13b but presumably lower than $19.8b.

Still, I think it is unlikely that the value of Pilot doubled in the 6 years between the initial deal and the final deal, so it may be that Berkshire was not sure enough of the outcome of a lawsuit, and decided to accept a higher payout in Tranche 3 (based on the original terms of the deal) than what might have been obtainable.