During the Galactic Civil War era, the Galactic Empire utilized Gradient Seven, a detainment moon, as a prison facility. The Imperial prison barge known as Purge was dispatched in 1 BBY with the intention of delivering inmates to Gradient Seven, but it failed to reach its destination.
In June of 2015, Jason Fry, who collaborated on The Essential Atlas, mentioned that the omission of Gradient Seven from The Essential Atlas Online Companion stemmed from its classification as a military codename.