Navy Rum" is not just a name for dark rum. Originally it was the name of a specific type of rum distilled for the Admiralty in wooden pot stills in lieu of the normal metal ones. The distillation of rum in wood imparts a truly unique flavor that can only be described as "full and rich," making most others bland by comparison. This flavor is unique to the wooden process and cannot be duplicated from any other type of distillation.
In today's spirits world, Pusser's is the only rum that is still distilled in the wooden pot stills of yesteryear, interestingly in the same original Admiralty stills. Rum that is not distilled in wood cannot achieve the unique flavor of a real Navy Rum. While others may have designated their product to be a navy rum by the mere inclusion of the phrase 'Navy Rum' on their label, they can never be a Navy Rum any more than a Rolls Royce logo placed on a Ford doesn't make a Ford a Rolls Royce. A real navy rum has to be distilled in wood.