Specific mention of the Black Watch and the line "Through Gibraltar to France and tae Spain" means that it had to date from a period after the Regiment came into being and from a time when Britain was at war with both France and Spain and a time when it was not present in Portugal.

That dates a phrase in the chorus and no more. The text Jeannie Robertson sang is from decades later. Songs change with time, and in this case the most interesting and creative parts of it aren't the oldest, and neither is the ironic rhetorical structure.