The Site Map doesn't show every single page on the site, it does try to pick the most important ones. Sometimes it can be helpful when using a site map to think in more general terms. For example, the map might not point to the sign up form for the Fall Ordeal, but it does have Forms.
The Site Map is prepared dynamically, and the dates are determined each time the page is displayed. Pages which have been updated in the last 30 days will show their update dates in red.