The NIST-JANAF Thermochemical Tables website is on an online resource that contains the contents of the NIST-JANAF Thermochemical Tables printed volumes. This website is a resource for sharing the data from the work that went into producing the volumes, not as a resource for the most up-to-date thermochemical data available. This is intended as a historic archive for an incredibly valuable resource that continues to have value today.
If you are interested in background information on the conntent of the NIST-JANAF Thermochemical Tables, you might find the introduction to Volume 1 of the Fourth Edition to be a great resource.
If you are interested in finding the most up-to-date thermochemical data, the Active Thermochemical Tables (ATcT) project hosted by Argonne National Laboratories (ANL) under the supervision of Dr. Branko Ruscic may be helpful.