Суть проста. Империя начала исследования, ПО продолжил их (или получил уже готовенький проект) и построил Старкиллер. Ни о каких технологиях цивилизаций из неисследованных регионов ни слова. Таков канон. Нет, мыши могут запросто переписать всё сто раз

STARKILLER BASE
The Empire's military technologists continued their research into apocalyptic energy weapons even after the regime had surrendered. After retreating into the Unknown Regions, Imperial survivors found fragments of experiments undertaken by the Empire that could be combined and refined into an unthinkable weapon. The tapping and storage of quintessence energy; the expulsion and amplification of that energy through hyperspace; the construction of a platform large enough to support such a weapon-these elements became Starkiller Base. It took decades to perfect, and many uncharted worlds in the unknown were cored and sacrificed in pursuit of this knowledge. The Starkiller fires only once, but its single blast wipes out the New Republic capital, undeniably demonstrating the First Order's power.

FIERCE MACHINE
Properly energized, kyber crystals create containment fields that hold and amplify power to incredible levels. The Empire controlled several kyberrich worlds, funneling their resources into the Tarkin Initiative's Death Star development. One unique world in the Unknown Regions, llum, had a kyber crystalline core. Most of its more easily accessible deposits were sCoured, but there were even larger crystals buried deeper beneath the surface. The First Order continued its excavations and gradually transformed llum-a revered Jedi world since antiquity-into an instrument of unfathomable destruction.

30-0 BSI* Starkiller weapon development progresses in Unknown Regions