One thing that should be clearer from my notes on Furthest as well as the Guide to Glamour is how little most Lunar cities resemble the First Age settlements of GRoY. Most outside of the Tripoli’s and a few other enclaves like Jillaro were rebuilt in the Fifth Wanes. A good point of comparison would be the Hellenistic cities of Alexander and the Successors, most of which were built on older foundations.
The TLDR version – don’t overly rely on GRoY to get a feel for the modern Lunar Heartlands.
GRoY is the acronym used for Glorious ReAscent of Yelm, which was a deep background sourcebook by Greg on Dara Happa. It was set in the early First Age, so a good 1400 years before the present.
To understand the modern Lunar Empire you don’t need to refer to GRoY. You might get some interesting glosses based on them or some near little story ideas. But don’t try to throw every element or name from them into your description of the modern Lunar Empire.
Do you assume that current Lunar cities are built on tells composed of the ruins of previous cities? Many certainly are. Sheng Seleris and his nomads demolished and depopulated Karasal, Oronin, and much of Doblian satrapies to create the “New Grasslands”. Same thing with Vethil and Oraya. Those cities were in large part refounded in the Fifth Wane – that’s the “Restore and Rebuild” area on page 171 of the GS. The ruins were stamped down and a new city built atop them.
Areas under direct control of Glamour, Jillaro, Alkoth, and Dara Happa On Horse were left more intact, although even many of these cities were the focus of rebuilding, if only to remind everyone of the Red Emperor’s victory.
The “New Grasslands” were just that. The depopulation of that area was similar to the destruction of Khorasan under the Mongol conquerers.
I think it is more like the incorporation of older elements in the monumental architecture of the Successors. Ptolemaic pharaohs, Seleucus having elements of the Esagila transferred from Babylon to Seleukia on the Tigris.
So Lunar rulers take older reliefs and use them or make new versions of them. Of course, they are free to change the iconography. Like how Arsinoe II or Cleopatra VII got depicted as Egyptian goddesses.