Point #2 is a load of bollocks, notwithstanding any so called "custom of the service" nonsense. I do not address corporals as "Sir" regardless of whom they purport to represent. I always use the appropriate form of address of the person to whom I am actually making the declaration and no one has ever called me on it. What would they do if they did want to call me on it, charge me with insubordination? That would make for an interesting court martial - "...insubordinate in that he refused to address his subordinate in the manner befitting that subordinate's superior, an unknown officer, who was not present at the time,...."
Furthermore, not saying, "Sir" does not make the declaration any less binding. Somehow, I don't think, "well I never properly declared to the OCE that I didn't have any live rounds or empty casings in my possession, because I didn't say Sir to the corporal," would be a winning defence strategy at a court martial.