>>23574018 (OP)
It's after a version of UC that had various Space Wars, lost all the colonies and had a huge space elevator. So, it's really hard to give any dates, because it's clearly not the setting as shown in Victory or any other late UC work for example. We don't know for how long this "UC" went on.
Like already mentioned, Tomino actually intended to set it after Turn-A (and consequently the Dark History) and if you look at that all those events make sense (Various space wars, colonies leaving, space elevator, country names) were all elements from Turn-A's past (and note Turn-A's script itself also referenced the Dark History as a whole as "Universal Century" at times, even though Tomino told the staff to add references to the AUs too). Bandai/Sunrise didn't seem to realize that was Tomino's intention with G-Reco until after he talked about it in post-series interviews, which is why the visual references are UC-only this time.