Adding featured images to "all posts" admin page for custom post type

I have two custom post types and I wanted to show the featured image on the “all posts” page in the admin for both CPTs. The first one is “agents” and the second one is “commercial-sale”. For agents, I have to add these two lines of code to my plugin to show the featured image:

add_filter("manage_edit-agents_columns", "post_edit_columns");
add_action("manage_agents_posts_custom_column",  "prod_custom_columns");

If I omit either of these lines, the preview image will not show up.

For the “commercial-sale” CPT I added similar lines of code to to my plugin:

add_filter("manage_edit-commercial-lease_columns", "post_edit_columns");
add_action("manage_commercial-lease_posts_custom_column",  "prod_custom_columns");

But doing this makes the preview image show up twice. If I comment out only the FIRST line, I don’t get any preview image at all. If I comment out only the SECOND line, then I get a single preview image just like I would get for the agents CPT.

Can you help me understand what’s going on here?

Thanks!