In 1978 Japan's Ministry of Economy, Trade and
Industry
established the encoding that would later be known as JIS X 0208, which still
serves as an important reference for all Japanese encodings. However, after the
JIS standard was released people noticed something strange - several of the
added characters had no obvious sources, and nobody could tell what they meant
or how they should be pronounced. Nobody was sure where they came from. These
are what came to be known as the ghost characters
(幽霊文字).
The article only details the first one, 妛, which happens to be a literal paper cut and paste that was misread, and the last one, 彁, that was possibly a misread from a similar looking character. Would’ve been nice if it explained some of the others