This archive tracks four layers. A record present in 2 of them (M41, IND) is silent in the rest, and says so.
The Horus HeresyM30–M31
[RECORD LOST]
No record for this location in The Horus Heresy.
Age of the ImperiumM32–M40
[RECORD LOST]
No record for this location in Age of the Imperium.
The 41st Millenniumpre-Rift
chaos
The Planet of the Sorcerers
The world Magnus pulled his Legion onto after Prospero burned, held together by sorcery inside the Eye of Terror and reorganised into cults rather than companies.
Era Indomituspost-Rift
chaos
Thousand Sons homeworld, back in realspace
Drawn out of the Eye and into the Prospero System when the Rift opened, so that the Thousand Sons now hold an empire inside Imperial space from the system they were driven out of.
Contested record
Position by era: Lexicanum's infobox lists Segmentum Obscurus (its Eye of Terror address for ten thousand years) alongside System = Prospero System and Sector = 'Prospero Sector (previously Eye of Terror)'. The record uses the post-Rift Prospero position; before M42 this world was inside the Eye.
Position
Map frame: 596, 385 in the archive's 0–1000 disk space (core at 500, 500).
Distance from the core: 150 units ≈ 15.9k light years, north-east of the galactic core.
Height above the disk plane: 2.6 units — invented thin-disk jitter, deterministic per record. No published source gives any location a z coordinate.
Every fact in this record, and where it came from. Editorial derivations say so.
segmentummedium
wh40k.lexicanum.com/wiki/Sortiarius infobox Segmentum = Segmentum Obscurus, but the SAME infobox gives System = Prospero System and Sector = 'Prospero Sector (previously Eye of Terror)'. The two fields contradict each other; the Sector field is the one that carries the M42 change, so this record is filed in Ultima with Prospero and the conflict is flagged disputed
derived: identical to Prospero's, since the infobox places it in the Prospero System. Its earlier position inside the Eye is not modelled — this dataset carries one position per record. Corroborated relationally: GW's official Era Indomitus galaxy map draws Prospero and the Planet of the Sorcerers co-located, which is the handling this record already used