Maze☆Bakunetsu Jikuu: Tenpen Kyoui no Giant

Anime digital archeology.

Lost: For media that is completely lost.
Partially Lost: These pieces of media have had over half their content found.
Found Media: Media that was once lost, but now found.
Partially Found: Media that's had up to half of its content found is listed here.

Every cinema or direct to video anime film that came out in 1998.

1997: https://myanimelist.net/stacks/34763
1999: https://myanimelist.net/stacks/34771

Anime that are partially or fully lost.
Notes: I’m not including series that are only missing dubs. I’m not including anime that were previously lost media but have now been found. There are many series that I have been unable to find in the MAL database and therefore have not included. And, lastly, the information in this list is sourced from the Lost Media Wiki.