At first, please read my previous review about the more interesting sequel, Corpse Party: Tortured Souls - Bougyakusareta Tamashii no Jukyou
(https://myanimelist.net/reviews.php?id=303031)
About Corpse Party: Missing Footage, it represents a slice of life mini-episode showing every character we met in the main story. Ironically, it gives more screen time and information about useless characters. I might sound harsh saying so, but it was plus or less the case. Indeed, we kinda knew nothing beside relations between characters. That made me having trouble feeling empathy, fear or pain for those (except for Yuka, who finds a terrible fate).
This OVA was no more but an introduction to the 4-episode anime/OVA that brought blood, guts and horror. It should be watched before watching Corpse Party: Tortured Souls - Bougyakusareta Tamashii no Jukyou.