There are supposedly only 72 Gundams in this timeline, all made during the Calamity War 300 years ago. Their defining characteristic, the Ahab Reactors, provide them near-infinite power supply and operational duration, something of an equivalent to (true) GN Drives of 00.
The name and number of Gundams in that universe (as seen thus far) corresponds to the 72 demons in Ars Goetia. My guess is that this time, they're going for the "Demon Lords" of the Old War angle.
