Language is easy, spaghetti code written without any discipline 60 years ago and modified in haste since is hard.
When we needed changes (this was back office clearing stuff for a bank) they wouldn’t even talk to us until we specced out the changes we wanted in writing and often the specs we submitted would come back with requests for clarification. This was like the opposite of agile, but I don’t recall any bugs or defects making it into production.
Modern software engineers would hate that kind of red tape because we've been conditioned to want shorter feedback loops. Heck, I hated it back then too and I wasn't even accustomed to seeing my results instantly like I am now. It takes a special kind of person to enjoy the laborious administrative overhead of writing detailed specs before you write even a single line of code.