I worked with COBOL long before DB2. I also worked on the COBOL compiler in the 70s. Unless things changed drastically if a value wasn't initialized the compiler left garbage in the variable when the program was loaded. If you were lucky this caused the program to ABEND when you tried to use it, if no ABEND you got strange results. It was up to the programmer to set a default date if one was required by the application. Many applications started with VSAM which did not care if a date in a record was invalid. This caused many systems to set default dates when converting to DB2. DB2 does not allow garbage to be loaded into a date field. COBOL does not initialized data unless instructed to do so.