Exactly this. Back pay maintains the principle for those that retired or left but performed work for parts of any year after the amenable date. If it were to only cover inflation (or a modest amount above it), then it also wouldn't be a huge windfall (likely less than the signing bonuses at Alaska for many). This is also probably much easier to explain to anyone who isn't a pilot, "X percent for 2020, Y percent for 2021, Z percent for 2022." It also has the added advantage of making new rates in the contract not look obscene to other work groups, etc. If the baseline is moved for the previous years via modest increases, then compounding interest would make a less eye-popping percentage increase for 2023 actually pay out more.