Crime scenes of the 6 linked closed rooms

Axioms

While she doesn't repeat it in red every time, all six rooms will be assumed to fit Beatrice's definition of a closed room.

Banquet


Alliance


Discovery Character Room
1. Shannon Parlor
2. Kumasawa 2nd floor guest room
3. Gohda 3rd floor waiting room
4. Kinzo Boiler room
5 Genji 2nd floor VIP room
6 Kanon Chapel

Corollaries

All the rooms where (at least) a servant with (at least) a key has been found, are linked closed rooms.

Even if we suppose "the linked closed rooms" only include five rooms out of the six, and we collapse Shannon and Kanon into Sayo, she still must have died in one of the 5 rooms.
We solve this by semantically declaring Kanon and Shannon dead despite Sayo being alive like we did in Turn. She was shot during a disagreement and is wounded, and according to the red they only appeared to be fatally wounded.

Additionally, a 7th unconscious person being present out of sight next to Sayo solves it (not hiding, just unconscious).

Other points of flexibility are the definition of the word "corpse" and "The linked closed rooms" possibly being be the name of the mystery and not a property of the rooms.