I am considering qualifying for COPA Presidential status instead of United 1K status during 2020, but I'm not sure if I understand how the upgrade certificates awarded by COPA are used on United flights. If United.com shows "Z" inventory in advanced mode, does that mean I can confirm an upgrade on that United flight using COPA regional/global upgrade certificates? If yes, that seems WAY too good to be true. United "Z" inventory is discount paid business class and is very often available. Or is the "Z" class required by COPA for applying its upgrades something different, like United's "PZ" fare class (upgrade inventory for its own PointsPlus system) or United's "ZN" (non-elite everyday award space under United's old award system)? I don't want to earn COPA status and then learn the hard way that it is all too good to be true.