No luck but I sincerely thank you for trying. I have a support ticket sent to ACF to see if they have any insight. I’ve also tried a number of similar code snippets found through searches but I can’t get anything to change.
Just to be clear, I’m expecting the Excerpt field at the bottom of the post editor to be populated with the year field. I have another plugin that will only use the Excerpt field to display data alongside the post title. Maybe what’s happening is the data is being passed somewhere that I can’t see?