The PCV (Positive Crankcase Ventilation) valve, came about sometime in the sixties IIRC, it was a measure taken in an effort to reduce air pollution.
Before that, excess crankcase pressure was vented into the atmosphere through "breathers", either on the valve covers, or sometimes through the oil fill cap...
This has been a presentation of "Your internal combustion engine & you, the early years"...![]()