Even your online directory is out of date!
Back in the day of printed directories, there was an aphorism: "By the time your directory hits the street, it's already out of date." This was because the data had been collected six months in advance, then had to be collated, designed, sent to the printer, reviewed in blueline, printed, shipped... You get the picture.
So we moved to online directories, where the data on the website is connected directly to the website in realtime. Problem solved, right? Well, not exactly.
Your online directory is still out of date. Because people change jobs and don't tell you. They leave the industry and don't tell you. They die and don't tell you.
So why do we bother if it can't be 100% accurate? For the same reason we printed directories that we knew wouldn't be 100% accurate: because success is better than perfection.
We should always be working towards better and cleaner data. After all, there is no stasis in data management. But we also need to keep in mind that success is achievable, while perfection is not.