Interest Stacks

Lost.
Presumably released in mid/late-1998

Was available in Makoto Shinkai's website till early/mid-1999 due to bandwith issues. Due to the antiquity of the site, nothing can be found in archive.org other than information and screenshots of the short in a snapshot from 2003. Shinkai himself states that he does not remember what the short is about, and he only made it to practice 3D animation.

There is some "recreation" made with the screenshots found at the site.

Found media (c. 2015).
Unconfirmed existence of an unreleased sequel.

Lost. Mentioned in a video of Kenny Lauderdale.

Completely Lost. No info about this short can be found. Has a sequel that is found.

Completely Lost. Almost no information about the program can be found either. An auction of a CD with its soundtrack can be found.

Completely Lost. Almost no info about this short can be found.

Completely lost.
The entire movie was never completed, only a preliminary teaser is available.

Completely Lost.
Release date is unknown, presumably between 1972 and 1979.

Lost.
Only trailer available. Supposed to be a 2 episode ONA but the existence of said episodes is unknown.

Completely lost. Only Trailer available.

This Korean movie is notable for being a co-production between North and South Korea.

Found Media (1990)

Partially found.
1 out of 39 episodes found. Existence of a 40th episode is unconfirmed.

Found (c.2021).

Was available on Youtube from 2015 to 2017.

Lost.

Apparently it was only screened at an event but no footage can be found.

Lost.

Only the PV exists.

Lost.

Aired only once in TV Asahi in 1979.