Re: frozen milk and fresh milk???
Fresh milk can be stored in the fridge for 8 days, so it isn't always necessary to freeze it, depending on when you need it.
Previously frozen milk can be stored for 24 hours in the fridge.
Fresh milk can be added to previously frozen milk, as long as the frozen milk remains the larger part and you refrigerate the fresh milk before adding it (if you want to put it back in the freezer).
I would start using the older milk and keep storing the fresh milk.