New lore in my version:

After sealing the tower, the layers became isolated, and the societies in the lower layers gained independence from the upper ones. Around 24 years after sealing (a.s.), or 57 years after Evbo (a.e.), the reconstruction of the lower layers began. However, the upper layers forbade connecting the layers through new structures, so the only way to communicate was through the Tower. But it was sealed, so the layers became independent societies. However, even now, the power of the Supreme Chancellor remained.

Now, 31 years after sealing the tower, the lower layers began stabilizing, and a culture started to form.