There are a number of unmaintained documents, which can be found at: http://metalab.unc.edu/pub/Linux/docs/HOWTO/unmaintained/.
These are kept around since old documentation is sometimes better than none. However, you should be aware that you are reading old documentation.
If the date tag is too old, please consider the HOWTO as unmaintained.
However, there are exceptions, such as old programs (for example UUCP HOWTO) or not-so-hot topics (for example AX-25 HOWTO).