There is no “date” data type in COBOL, but there is in DB2, where the data would be saved, unless they are on an older VSE OS and data is still saved in VSAM files. Many still use 12/31/39 as a default max date even though OS/400 systems can handle up to year 9999 now (we still use 12/31/39 in testing where I work). It could be someone arbitrarily started using 1875, and others copied that.
There is no “date” data type in COBOL, but there is in DB2, where the data would be saved, unless they are on an older VSE OS and data is still saved in VSAM files. Many still use 12/31/39 as a default max date even though OS/400 systems can handle up to year 9999 now (we still use 12/31/39 in testing where I work). It could be someone arbitrarily started using 1875, and others copied that.