Forged steel parts are surprisingly resilient to corrosion. That's why so many Ford tools survived to be found in garage sales and at the flea markets. They could have used a black phosphate finish which is still common for unplated tools but they opted for what they were already using in house and from the sub contractors. A person could phosphate finish them for a longer lasting effect if they choose but for all intents and purposes, anything that protected the tools for a few years mostly riding around in the trunk of the car or under the seat in a cobra grain tool bag was considered to be adequate at the time.