These holes were no longer required after the AA handle became obsolete in 1940 and so were omitted during production. Those that had the AA handle clips from manufacture had them removed and discarded leaving the holes open. Being 80 years old it has a couple of coats of paint and lots and lots of heavy small arms oil in the joints and AA leg.
Please note this is not one of the hundreds of common Australian AGE tripods in the UK, it is a very rare British BSA made, Enfield Accepted Mk1 AA tripod. Try Googling BSA Bren tripod and see how little there are in existence.
In 30 years of collecting Brens I have likely only ever found about 20 genuine BSA Mk1 AA tripods but seen hundreds of not thousands of AGE. The item "Rare Early Bren Gun Anti aircraft Tripod Mk1 Made by BSA 1940 Enfield acceptance" is in sale since Tuesday, October 27, 2020. This item is in the category "Collectables\Militaria\World War II (1939-1945)\Field Gear". The seller is "al1son0" and is located in Sleaford. This item can be shipped worldwide.