hooks names with no associated actions

Yeah the majority of the time these are events left over by old plugins. The name of each event hook should give you an indication of which plugin they might belong to.

That said, I’ve seen a small number of plugins which only register their cron event handler when the WordPress cron event runner is actually running, which makes it impossible for WP Crontrol (or any other WP-Cron management tool) to show the associated actions.

Googling the cron event name usually helps figure out what it belongs to.