Here and there, Chaotic United will make legacy versions of websites readonly but viewable to the public. An example would be the Chaotic United forums before Nuclear District announced its closure, or the old United AlyCraft forums. Another example is the old Chaotic United website, seen here: http://chaoticunited.net/classic. Sometimes, we may have internal legacy websites that exist somewhere on the webserver but are never shown to the public. Very rarely is this the case, but when it is it is usually due to copyright or legal reasons, or in some cases, our of genuine respect for the creator's wishes. They are usually kept on hand for content reusability, for instance if an older website had a feature or page, or a page style or layout that we feel would blend well with the existing website layout. But sometimes even then, we just keep them online so we can relive some nostalgia. Which is the main reason you see any public legacy websites to begin with.
Legacy pages can mean a couple of things. It could refer to a page that is no longer updated, or a page that is no longer required, for instance if its functionality has been replicated elsewhere. These legacy pages will still work by all means, it's just that they are no longer updated. Sometimes, these pages can be skipped over or unchecked during site upgrades. While many times pages will work, sometimes things can cause specific legacy pages to either break visually or functionally, thus rendering them unusable. Some examples of these pages are the CU and ND staff pages, the CU page being replaced with the staff list in the About page, and the ND one being discontinued as Nuclear District is closing (though I wouldn't be surprised to see some return of those 3D skins in the future).
List of Legacy Pages