Aside from flashbacks, this was the only appearance of the Halla's [ED- in the letter column of Green Lantern Corps Quarterly #4, the editor alluded to an upcoming story involving "one of the first Green Lanterns picked by the Guardians (in a time before the rings came into existence and the emerald warriors wielded guns)". Presumably, he was talking about the Halla's. The story was never published]. Though they were established in the GL mythos in 1976, six months later they would be overshadowed by a story in JLA # 140 (March 1977) which introduced the android Manhunters as the predecessors of the GLC.
The Halla's claimed to have been active four thousand years ago, but this is unlikely. The Corps became active over three billion years ago. In all likelihood, the Halla's' starship chronometer had broken in their three billion year slumber.
Mike Grell used a lot of influences from Star Trek (back before it became known as "Classic Star Trek") in his Green Lantern run. The Halla's' ship looks like a Klingon warship. The "stun guns" of the Halla's are hand held phasers. Earlier in this issue, Hal Jordan had been talking to Saarek.