The thing about most old COBOL is that there is very little shared code. There are things called "copybooks" which are snippets that get copied into your progra

The thing about most old COBOL is that there is very little shared code. There are things called "copybooks" which are snippets that get copied into your program at compile time, but they are not "shared" code. So you have much less chance of affecting anything else when you change a COBOL program. Most are written to perform a single transaction or generate a single report or screen, and are entirely self-contained.