Data structures were once designed to suit a specific purpose, not just to comply with compilers. The constraints for valid dates, particularly for Social Security benefits, can be traced back to the introduction of the program in 1935. This led to the logic of using 1875 as a base year for date entries in order to optimize data storage on punch cards. While some claim that COBOL defaults to 1875-05-20 for corrupt dates, this is not supported by technical evidence. The practicality of using this method is highlighted for commercial applications during the mid-20th century. This unique approach to storing birth dates is a product of early data processing methods and space-saving techniques.
https://retrocomputing.stackexchange.com/questions/31288/does-or-did-cobol-default-to-1875-05-20-for-corrupt-or-missing-dates