So if Duty Manager's leave, who locks up and alarms the store at night? The Supervisors?
I am the only person who is a Key holder who is a non duty manager (apart from the bakers) at my store, that's mainly because I'm only a 2 minute drive from work and second on the call out list (SM first).
Your store must have a lot of trust in the Supervisors to give them Safe numbers. Here, only the SM, SSM and Duty Manager's have safe numbers. We have a pin pad and also spin dial, which a few years ago only the bakers knew the combination of the spin dial, and everyone else only had a combination for the pin pad, so at any point in time you needed two people to open the safe. But that was eliminated a few months ago.