The original meaning of the word formula related to the ratio of water, sugar, and evaporated milk you would feed your baby. It was literally a formula, a recipe.
Along with the evaporated milk, babiesin the US were fed orange juice to counter the constipation they would suffer from the evaporated milk /water/ sugar mix.
Spme doctors definitely knew about CMPA back in the 60s - my two sisters were diagnosed with it and had a goat milk formula instead, which mum bought in powder form and mixed with boiled water. This was in Ireland so I doubt it was unknown in the UK.
When DD1 was born in 1990 (in the US), exMIL was puzzled by the lack of cans of evaporated milk and orange juice in my apartment. I was baffled and couldn't understand what she was going on about. She had apparentmy fed all her babies evaporated milk, water, and sugar, plus orange juice. They all survived, but holy crap, what were doctors and parents thinking ...
My mother had never heard of anything like it.