No problem, I am glad to have been of help.
Your assumption around the event handlers is correct. The shortest explanation I could give you on this is that ‘axon will look for the most specific event handler for a given event’.
Thus if you have an Event Handling Class with both the Parent and Child events being handled in it, a ParentEvent will always be handled by the ParentEvent Handler and vice versa.
But if you have an Event Handling Class with only a ChildEvent handler in it, that handler will both handle the Parent and Child event, is the ChildEvent handler is 'the most specific handler for that given event based on class hierarchy.
Your use case with the command handling doesn’t sound to weird.
Sadly though, like I pointed out, this message hierarchy does not work for command messages, only for event messages.
I’d thus suggest to have a dedicated command handler for your SaveApprovedCertificateCommand.
Much luck and fun furthering your experience with the framework, and please keep us apprised of any questions you might have!