These were deficiently announced/advertised compared to other ports or other games of the same publisher; Hidden in their package; obscure on publisher's homepage, etc
The first video game about Obscure Release was released in 1988.
Note, if a TV ad aired, or ads appeared in print, or it appeared in the publisher's catalog, in similar settings and/or like manor as other games from publisher, then don't use this tag. For example, Pepsiman for PSX had a commercial in Japan. Shareware games should almost never have this tag either.