A little late to reply to this. I think the answer to the missing avenues was the depression, council ran out of money. My parents lived in the avenues from about 1934-5 and I left in 1954. There were stub roads at the top of 6th and the back of 12th on Newlands road which would presumably have led to the missing avenues. Newlands bungalows were privately built, my uncle was living there in 1936.