Hi @dtomasch
I believe you can order the posts based on the date picker field. This page should give you more idea about it: https://www.advancedcustomfields.com/resources/orde-posts-by-custom-fields/.
You can also query the post to get only the last four years. Please take a look at this page to learn more about it: https://codex.wordpress.org/Class_Reference/WP_Query#Custom_Field_Parameters.
By combining those queries, you only need to loop the posts and check the event’s year.
I hope this helps 🙂
