I rewrote a product which was not working and was never completed 100%. New version is better but I had to hack things here and there due to constraints of the

I rewrote a product which was not working and was never completed 100%. New version is better but I had to hack things here and there due to constraints of the existing systems. Additionally, the number one problem is lack of documentation, not in the app but in the business sense. In order to write a good application the process it is going to support needs to be well documented. This wasn't the case and I had to go back in circles a few times but you live and learn.