The period of no sidhe nor True Fae on Earth, with the remaining 'watered down' changelings having to fend for themselves after the final death-throes of the Shattering around 1400 AD is the Interregnum, as changelings had to try to work out how to survive on their own. A very rare few still had occasional access to the Dreaming, but Arcadia was either completely detached from the Mundane World or perhaps as some rumoured, had been destroyed. The sidhe and True Fae in Arcadia also didn't know if the Mundane World had survived the Shattering, some believing that its time had ground to a halt.
After the Shattering, the changes in human and fae society were immense. Mortals rediscovered ancient Greek and Roman thought and moved from religion to science and rationalism as the underpinnings of their lives. The Age of Exploration and the Age of Invention fed upon each other and found new worlds and ideas to explore. Peasants became workers and monarchs industrial barons. Rapid progress and social upheaval were the norms.
The fae, encased in mortal flesh and barely connected to their fae selves were equally changed. The social systems that based themselves upon the sidhe were gone and with it the structure many had relied on. They banded together in small groups for protection, hiding their true natures from the Sons of Adam and Daughters of Eve as well as each other. The Seelie and Unseelie even struck an agreement, the Compact, to maintain cordial, if at times strained relations for the sake of survival.
Many fae found the growing cities too difficult to navigate and became wanderers; moving from village to village in traveling circuses, as vagabonds, and minstrel groups. The fringes of humanity, with their "freaks" and misfits were prefacer places to hide and induce in the creativity that sustained their fragile ties to their faerie natures. Many terms for Changeling Arts and customs come from this theatrical, circus time. Old ways die hard, though, and the fae still craved the nobility to add structure to their lives and many commoners rose up to fill that void left by the sidhe, taking over what fiefdoms they could.
For 400 or so years the Commoners fae made do with what they had and adapted to their new world.