This archive tracks four layers. A record present in 4 of them (HH, AoI, M41, IND) is silent in the rest, and says so.
The Horus HeresyM30–M31
imperium
Homeworld of Sanguinius and the IX Legion
A world of red rust deserts orbited by two irradiated moons, all three poisoned in a war that predates the Imperium. The Blood Angels take their recruits from the tribes that survive out there.
Age of the ImperiumM32–M40
imperium
Blood Angels homeworld
Chapter homeworld and the centre of a scattering of successor Chapters that all trace back to Sanguinius.
The 41st Millenniumpre-Rift
imperium
Blood Angels homeworld
Unchanged and unforgiving; the Arx Angelicum stands over deserts that kill most of the aspirants who cross them.
Era Indomituspost-Rift
imperiumImperium Nihilus
Besieged; intended capital of Imperium Nihilus
Hive Fleet Leviathan came within an ace of consuming Baal and its moons before the Indomitus Crusade arrived. Dante now rules Nihilus as Regent and means to make Baal its capital.
Position
Map frame: 620, 285 in the archive's 0–1000 disk space (core at 500, 500).
Distance from the core: 246 units ≈ 26.2k light years, north-east of the galactic core.
Height above the disk plane: -5.4 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.
segmentumhigh
wh40k.lexicanum.com/wiki/Baal infobox Segmentum = Ultima Segmentum; https://wh40k.lexicanum.com/wiki/Baal_System places it in the Red Scar region
classhigh
wh40k.lexicanum.com/wiki/Baal infobox Class = Adeptus Astartes Homeworld, Death World; 'a world of red rust deserts'
gposmedium
derived: northern Ultima Segmentum ('much of north and north-eastern Ultima is stranded in Imperium Nihilus'), placed north of the Rift line and still inside the Astronomican's reach, since Baal was a fully connected Imperial world before the Rift