There is a particular trope - and I'm not sure the name for it right now, sorry - which deals with an Outsider, usually a time traveler, going through actual history and interacting with it (sometimes changing, sometimes being proven unable to change it).
It's a little bit of Been There, Shaped History, a tiny bit of Field Trip to the Past. And the catch here is that the device involved isn't time travel per se; it's the unnatural longevity of one character who touches these stories (so he does travel in time, forward, at the same speed as everyone else, but for a much longer period).
In the comments @Hypnosifl suggests that it sounds similar to Secret History; I don't personally think so because it is not in essence revisionist; it proposes subtle influences to things that we know happened as described rather than suggesting we've been misled about what happened. But there's definitely some sympathetic resonance there.
The Baroque Cycle and Cryptonomicon are both stories in this trope; the only exception is that the Outsider is a character and not, by and large, a first person protagonist. Enoch Root is a man out of time, or a timeless man, or an angel, or a successful alchemist... whatever he is is not mundane, and he's woven throughout all of those books. He shows up for important points and has influence (e.g., providing advice for the teaching made available to the boy Isaac Newton, guiding Randy toward an understanding of how to wield Golgotha).
I guess I would sum it up as saying the Baroque Cycle is a very mild alternate history but, since there's an character with some sort of eternal life/resurrection magic that seems to be sufficiently advanced technology, that qualifies it for Science Fiction.
(Cryptonomicon, of course, is a little less history and a little more science, but again, Enoch Root has the only magic technology)
