The short answer has to do with expensed IDCs going through the excess IDC calculation to determine whether there's an AMT adjustment. Prior-year expensed IDCs get amortized for AMT purposes as part of the well-by-well calculation of what I'd call for clarity purposes tentative excess IDCs (as opposed to the AMT adjustment for excess IDCs).

Consider this a "you cannot rely on plugging tax form numbers in and assuming that a completely correct tax return will magically pop out" flag. Your guy has plenty of O&G income and plenty of taxable income and no actual AMT adjustment for excess IDCs? Judiciously override / delete / otherwise force the right answer. All that stuff sounded like gibberish? Time to do some research to determine what the right answer is.

Personally, I consider the auto-generated entry for K-1 O&G income (as opposed to O&G screen amounts) to be unhelpful and delete them first thing after proforma, but my affected clients could have enormously more IDCs and excess IDCs before they'd actually have an AMT adjustment, and with the SALT cap, could have enormously more AMT adjustment before they'd pay AMT. So "this has zero chance of materially affecting the correctness of my tax return" is the primary driver of that decision; your clients may vary!