I had the fortune to work on COBOL software for brief period of time at my last job, which was at a financial clearing company. This group of 50+ COBOL applicat

I had the fortune to work on COBOL software for brief period of time at my last job, which was at a financial clearing company. This group of 50+ COBOL applications that was the lifeblood of the company and a bad run could cost the company millions. The software was started in the early 90s, so it was easily 20+ years old when I was working on it. There was very little documentation regarding the process and the people who worked on the system were gone. I bring this up because when you have software that old you typically aren't going to have the original people who wrote it at the company nor will you have the people who gathered all of the requirements. All of the knowledge that went into that product was virtually gone. You are at a known state but you now have to re-create the steps to get to that known state as I'm sure a lot of the domain knowledge around the product is not there anymore. Not only that, you now most likely have other sources consuming the output of the original COBOL application so you have to ensure that the other applications are able to consume the new data and that those don't break either.