These are accurate. There are many things that I have failed to find, for, as far as I can tell, all of the reasons listed there (often more than one at once),

These are accurate. There are many things that I have failed to find, for, as far as I can tell, all of the reasons listed there (often more than one at once), and probably more. There are some other possible reasons, although most of them could probably be classified as one or more of the reasons listed there. There are some more possibilities (some of these can probably already be classified as the ones mentioned there): - It was communicated using the internet by a private (or sometimes also public) communication that has not been logged (e.g. a IRC or email communication). - It is indexed by search engines that you do not use but not by the search engines that you do use. - They use a CAPTCHA or other program that does not work on your computer. - You do not have version 6 internet. (This is an issue of the internet service provider, which does not seem to be one of the reasons they listed.) - You get a NXDOMAIN error when trying to access it. (This is a problem with the DNS service. This happened to me when trying to access some files using Gemini protocol. I was able to get it to work by asking someone else for the correct IP address and then adding them into the hosts file.) - Too many people disagree with it that it makes it difficult to find.