The Alcor connection to the Transcendence is pretty clear: the Transcendence happened, and then pretty soon after this dude named Alcor starts popping up. Fallers are pretty good about establishing that it was Bill that caused the near-apocalypse, and not Dipper; something that’s helped as magical texts and information become more disseminated/widely known/actually accepted as time goes on.
I think Mabel and Dipper are careful enough that the vast majority of people link Mabel to Mizar. Mabel and Dipper when they’re local try and take care to disguise Mabel’s face to some extent (a face mask, magic that blurs her face, et cetera.) When they’re further afield, it helps that they’re in places that lets be real, no one is going to have any idea what a Mabel is.
Perhaps some people make a connection between Mabel and Mizar, perhaps not (I’ll let this be squishy canon- let us know what y’all think!) but if we are talking the larger span of history, Mabel is probably mostly forgotten in context of Mizar theorizing. Perhaps occasionally a particularly determined researcher will produce evidence that Mabel Anna Pines was in fact, The First Mizar, but they aren’t taken seriously.