Just had a thought. Legend says that Xenogears was supposed to be Chrono Trigger 2 early in life before it got repurposed into its own thing. Which makes me wonder... maybe the six eras of time in Xenogears weren't intended to be six different games, like Xenogears fans have been thinking for two decades. Maybe they were intended to be time periods you'd visit in the one game.
It actually kinda lines up with CT having eras in time. Xenogears has six "eras" outlined in Perfect Works while Chrono Trigger has five eras you explore during the game.
The Far Past (Xeno) - No CT equivalent, but it takes place in space anyway, not on the planet. Wouldn't expect this in the game past the intro.
10,000 years ago (Xeno) = 65M BC (CT) - The genesis of humans on the planet
3,000 years ago (Xeno) = 12,000 BC (CT) - An ancient high-tech civilization is thriving, then collapses
400 years ago (Xeno) = 400 years ago (CT) - Near-past where a big war is taking place
Present (Both)
Future (Xeno) = 2300 AD (CT) - Future to see how things turned out
Never even really thought about this until now but I think it makes total sense that they fleshed out these eras to be the "time zones" of the game back when it was Chrono Trigger 2, then kept their work around for Xenogears Perfect Works etc while keeping the game firmly in the present era. This leading all of us to speculate for 20 years that they were going to make a six-game series or something. Nope, maybe it was time-zones for Chrono Trigger 2. My God.