"all providing 2 adjustable sight leaves, one for each barrel"

Kinda indicates the mechanics are for 'marketing' and the 2 sight leaves, one adjusted for each barrel takes care of regulation - much like a typical Kodiak muzzleloader, which has little or no regulation - & 2 adjustable sights, 1 sight for each barrel.

This was the method most used in the States for regulation of double barreled muzzleloaders, in around the mid 1800's as well, except that usually each set of sights were mounted on the top of each respective barrel. - reference "Firearms of the American West 1802-1865".