It has to do with the engine build date window. GM seems to have indicated they have determined a engine build date window of affected engines. So this does not include all 2021 or all 2024 vehicles. But will likely include all 2022-2023 vehicles.
For example, at least for the moment, my 2024 Yukon is not included in the Recall because my engine was built July 15, 2024. Initial engines included in the Recall were with engine build dates before June 1, 2024, then GM moved the date to builds before July 1, 2024.
I do not know the 2021 engine build cut date, but I am sure the window is or will be published at some point.
For example, at least for the moment, my 2024 Yukon is not included in the Recall because my engine was built July 15, 2024. Initial engines included in the Recall were with engine build dates before June 1, 2024, then GM moved the date to builds before July 1, 2024.
I do not know the 2021 engine build cut date, but I am sure the window is or will be published at some point.