I have frequently started working on products where there was little up-to-date documentation. You usually only notice it as you go. You might find that one part of the analysis does not describe the latest changes. As you find more and more inconsistencies, you will not be able to trust any of the documentation, even though some of it might still be ok. So why does this happen?
How does documentation become out of date and what can be done to prevent it?
If you are not making it, you probably recognize some of these issues: