Ann: Greater Pluto Reserves and Resource Update, page-30

That's not how reserves certification works. You can't add the 1P and 2P numbers to calculate a "net downgrade." 1P is a subset of 2P, not a separate volume. You don't add 1P and 2P to get total reserves. The upgrade to 1P is already included in the new, lower, 2P number.

1P is Proved reserves. 2P is Proved plus Probable reserves. In the previous reserves statement these were broken up as 287.9 MMboe Proved and 152.6 Probable (i.e. the difference between the 2P and 1P number, sometimes referred to as P2) for a total 2P of 440.5 MMboe.

In the revised number, Proved has increased to 317.1 MMboe but Probable has decreased to 77.8 MMboe, for a total 2P of 394.9 MMboe. As WPL said this is a downgrade to 2P of 10%.

The main reason the focus is on the 2P downgrade is because 2P is, by definition, the best estimate of final economic recovery of the project, because it's the midpoint of the distribution. The 2P number is the standard valuation for the base case of an economic analysis, the 1P and 3P numbers form the low and high side cases. The 1P numbers are essentially already banked in any valuation that's done on the 2P numbers, which is why there isn't much focus on 1P. You would expect the 1P number to increase (and the 3P number to decrease) as the field matures because more production history becomes available which narrows the range of uncertainty around the 2P number. This is what is happening here at Pluto - although they didn't release the 3P number, I'd be confident in saying it has dropped to reflect this narrowing of uncertainty.