AKHTUALLY
iirc, Turn A and X are supposed to be in the UC timeline too.They're just so late in it, and most of the records of what happened earlier are lost in-universe due to all the wars that they might as well be stand alone series. F91/Crossbone got rewritten in Super Robot Wars V to be a similar sort of "post apocalyptic" Gundam setup (for how little the game featured it). Well, I'm not sure about X since I haven't watched it, it could just be a retcon type thing that came later on for X, but I remember Tomino getting super mad that people couldn't immediately tell that G-Reco was set after Turn A despite there not being anything to suggest it plotwise.
For UC Gundam, there's a pretty clear through-line of
MSG -> Zeta -> ZZ -> Char's Counterattack
and I think that you probably need to see Char's Counterattack for Unicorn (and the things that tie into Unicorn) and the Hathaway movies (since it's an adaptation of a sequel of the AU novelization of Char's Counterattack) but for most of the other UC stuff you'd probably be fine watching it on its own.
(someone can correct me if I'm wrong, since I've pretty much only seen the original, 0080, Char's Counterattack, F91, and G-Reco out of UC Gundam, and I don't remember F91 very well)
The only certain death in the universe is Mother Hitton's Littul Kittons.
Not changing this line until I beat Seven Heroes (2/24/07) - Fulfilled 2/20/18