It is unknown whether the disc was sent out as part of a larger kit or if it was just the disc. It was sent to videogame magazines; the copy shown below was sent to a magazine in Greece. It contains multiple game assets, among them Eternal Darkness screenshots, artwork, and a video.
A GameCube lid sticker on the case covers the spindle hole area, completing the disc artwork. The disc seems to have been created on 2002.09.30.
1. Case with sticker
2. Disc
Thanks to eBay member vintagetoyscorner (images 1-2).