What is the difference between “manage_{$post_type}_posts_columns” and “manage_edit-{$post_type}_columns”?
It has to do with the way the admin post table is constructed. WordPress uses a class WP_Posts_List_Table to generate and handle that table. You’ll notice that there are a few tables in the admin area similar: Plugins, Terms, Users, etc. They each are their own class, but they all extend from a base class … Read more