No wire connected to breaker in main panel

I don't want to take anything for granted and it seems obvious that without any black wire connected to a breaker then the breaker is not in use. I want to confirm this. What puts some doubt in my mind is that there are two breakers without any wire. Maybe I am too orderly but I imagine an electrician filling each spot systematically and if there were two extra breakers left over they would be at the end and together, not in random spots in the panel. So, no wire connected; are they available for use?