The most reliable source of information comes from your trusted Real Estate agent. It is their job to know what is the most current and accurate information. Websites, although information rich, really should be compared to entertainment and very general in nature. They are best used to gather general information so that you are armed with questions, find and interview an agent, go from there.
The local MLS and Tax Records are pulled by all the virtual real estate websites. Not all these websites pull from the direct source, they may receive feeds only from individual brokers and paid data banks. If those sources are not pulling their data from the direct source, as it happens, then the information will not be accurate. Some websites, such as Craigslist, Zillow, and Trulia receive active listings direct from agents, so if the agent doesn't directly submit the listing, then it will not show up.
Real Estate agents and Brokers pull their data directly from the source.
Hope this sheds some light for you.