As my big post above suggests, the coreward half is basically stateless and volatile. There have been a few short-lived "empires" in the Dent, but the damage they wrought in subjugation and fighting each other is one of the reasons the Zhodani work to keep empire building from happening again.
The mash of opposed client states seen in the rimward half is a phenomonon of the last 3-400 years. Imperial exploration, internal strife and seccesion, Zhodani border securing operations, and the machinations of states further rimward* have made the political history of rimward Afachtiabr rather complex and chaotic since then.
The first state in the area was actually the Protectorate, formed in 536. The rest of the rimward half of the sector didn't really begin polity-forming until around 700. That's your looked-for period of Imperial exploration prior to state building, as the majority populace will be Vlazhdumecta "primitives".**
It is worth noting that Dale paints a somewhat different picture of the Vlazhdumecta than either the Yiklerzdanzh Project or I did. Looking at the differences, I can put most of them down to the absence of absorption efforts in Yiklerzdanzh compared to Afachtiabr, and the infusion of a violent streak with the arrival of the Sky Raiders. The Vlazhdumecta with some ambition migrated towards Yiklerzdanzh and likely repelled the Zhodani through sheer gumption. That history is elsewhere.
The Vlazhdumecta of Afachtiabr were more a case of mistakes made in the name of procedure. The Zhodani were probably waiting for the former colonies to either die out or regress so far that they would be overwhelmed by Zhodani cultural absorption. The regression occured, but not before a mad wave of last ditch recolonization put Vlazhdumecta colonies on every world that could support them. The folklore was also in place to make sure that every colony knew exactly why this was taking place. The fatalism of abandonment that overtook the colonies further rimward never infected the Dent, and the combination of superstition and a deep-seated racial tendency towards commerce (their "empire" had been primarily commercial, not military) ensured that the Zhodani who arrived later couldn't come up with "the right price" to make the Dent Vlazhdumecta accept cultural absorption.
What made the Imperial incursions in the rimward half of the sector go more smoothly than Zhodani attempts was the absence of cultural imperialism inherent to the Third Imperium's basic philosophy, and the influx of wealth their arrival brought to the "abandoned". Most Vlazdumecta in the client states area are relegated to the status of second-class citizen, but most also just don't care, since their lives are still better than they were before the Imperials arrived. Were I to speculate, I'd say the client states will someday get quite a shock when the local Vlazhdumecta get their collective ambition back.
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* the next sector rimward is The Vanguard Reach, an area originally developed (along with The Beyond, rim-trailing of Afachtiabr) in a rather wild fashion by Paranoia Press early in the CT days. The Beyond was publicly de-canonized by a dotmap in DGP's "Solomani & Aslan", but the Vanguard Reach remains a heady place of improbably high TLs, power politics, ruinous wars, wierd aliens, and a long history. None of it is Canon at this point, and the last time I spoke to Chuck Kallenbach (the original author) his map of the Vanguard Reach slopped over into Afachtiabr in ways that were utterly incompatible with Dale's work. I still regard the Vanguard Reach as a region similar to Chuck's version, just more Canon-compatible.
** whups! Seems Dale fooled me. The Zelphic Primacy was formed in Imperial year 58, but was alone until the Protectorate formed five centuries later.
