I've got a decent start on the abbreviation dictionary for the board that Skip suggested, but it is nowhere near complete (and also not 100% accurate). I will start a discussion with the first version soon, but the ultimate quality and completeness are going to depend on help from GHSers
BPO = Before Payout
APO = After Payout (Value of production minus Usually Drilling & Completion Costs AND also minus Lease Operating Expenses in some cases if it is spelled out in the lease)
The reason your statement shows APO1 and APO2 is usually because the company only wants to do one spreadsheet calculation for two different types of after payout interest 1) ULMO and non-notified companies who back in after 100% payout (prob APO1) 2) Statutized companies, etc who back in after 300% of payout.
At least that's how I have seen the yearly payout statements come in from the companies we do business with.