All the straightforward cases for WestJet PNR change are covered by online change, but there are a lot of edge cases that are not. Some of this is due to Sabre limitations, some are due to investment not being applied. Bear in mind that from a sheer size perspective, AC IT budgets are about 5 times larger and Delta 10 times larger than WestJets, yet the systems complexity are not that much different now between all three airlines. There is also the fact that Delta 100% controls their reservation system coding, WestJet doesn’t, neither does AC now. Since AC moved to Amadeus, they also lost automation in some cases that hasn’t been reimplemented yet in all cases.