The adjustment holes lines up with a wheel on the inside that spins and expands or contracts against the bottom of the brake shoes. I have never seen more than one adjustment hole. I can only guess that it is there for different applications and one of the holes actually gives access to the adjustment wheel.
1966 Mercury Park Lane 4 DR Breezeway 410 4V, C-6, 2.80 - Streamless.
1966 Lincoln 4 door Convertible 462 4V 1971 Ford LTD Convertible 429 4V Phoenix ~ Yeah it's hot however it's a dry heat!