It looks like the average bra size has been on a steady increase since the 1950s!

Chickens are 4 times bigger today than in 1950s

Bikini Style Trends History: From String Bikinis to Ancient Swimwear

Bra Sizes – A Thing of the Past

Bra Sizes – A Thing of the Past

When the body changes – the best bras for the mature woman

What's the deal with pointy bras in the 1950s? - Quora

The evolution of breast sizes: from the voluptuous 50s to the natural 00s. - Pietro di Mauro

Women's changing bust size – Bluebella - US

Exhibition: Lift & Separate: Technology and the Bra. Chapter 4

Women's changing bust size – Bluebella - US