You've never flown supplemental, have you?
With four pilots, what's the legal duty day under international rules (14 CFR 121.523)? 30 hours. Welcome to reality. You may have missed it, wrapped up in the cozy confines of Part 117, or the fact that the supplemental world was carved out of the duty and rest rules when introduced a decade ago. In other words, excluded.
Standard duty day for a two-man crew, domestic? 16 hours.
Three pilots domestic? 18 hours. International with three pilots? 26 hours.
Four pilots domestic? 20 hours. International 30 hours.
If that crew flew ICN-ORD with revenue cargo, however, and ended their duty day in Chicago, it's entirely possible that the next leg back to Incheon was done under Part 91, after duty. This is legal.
Not legal was what WGA was trying to do a few years ago with the 747 crews: Part 91 legs BEFORE duty. A chief pilot quit over that.
WGA runs it's MD11s under domestic flight, duty, and rest requirements, as it has no rest facilities on board, and does not do crew rest on board. Not so, of the 747, which can do international flight, duty and rest rules. WGA has also done a lot of Part 91 repositioning, ORD-ICN, or LAX-ICN on legs up to 14 hours, and they've done it with as few as two-man crews, though more often with just three.
For the bonus round, how much rest is required of a crewmember on their first duty day, before duty, in the supplemental world? If you guessed zero, and you'd have to guess as this is clearly foreign to you, you'd have guessed correctly. Go figure.
How much rest time is required "behind the door?" Zero, because this is an imaginary term not found in the regulation. Thus, when WGA commercials a crewmember to Anchorage for 13 hours, then gives 10 hours "rest" from arrival to departure, the crew member might take an hour getting to the hotel, typically shows two hours prior in the lobby, and has seven hours. If the crewmember selfishly wishes to eat, deduct a couple of hours to go get food, there's five hours. If one is stupid enough to believe a crew member can fall asleep, and wake up and prep in an hour, there's four hours of actual "rest" before the duty day, but let's face it. That's really not happening either, especially if one's the captain and will be getting up to prep for the flight, call each crewmember an hour prior, etc, to say nothing of the rolling delays pushing the flight back an hour, or three hours at a time, sometimes for another 12+ hours. WGA maintains, as do most supplementals, that if a crewmember is fatigued, he or she may call fatigue, but otherwise, the show goes on. Factor into that time zones, cumulative fatigue, and other things that Part 117 covers...but that supplemental regulations do NOT, and even a simple legal duty day may be a whole lot longer than a simple legal duty day, and a lot more exhausting than a mere 16, 18, 20, 26, or 30 hours. Factor in trips that fly west in which you fly all day but only see night, cross the dateline to return and land two hours before they took off, and trips that span two days and never see dark...and you may be a supplemental pilot. If any of that surprises you, then clearly you have never been.
https://www.ecfr.gov/current/title-1...-121/subpart-S