You've hit on exactly why mistakes in excel spreadsheets don't get corrected. Evveryone checks the output, many people check the results of intermediate calcula

You've hit on exactly why mistakes in excel spreadsheets don't get corrected. Evveryone checks the output, many people check the results of intermediate calculations, but in most cases people don't check the code if those are ok. Everything goes well until either the data changes enough to make the error in the code matter, or some other code is added which relies on assumptions about how the broken code works, and the sheet starts pumping out garbage.