Wyatt's telegram would never have made it. The disruptions to the timeline created by both Flynn and the team would have resulted in any number of changes that would have led to the telegram not being delivered. Western Union could have gone out of business entirely instead of repurposing itself as a money transfer service as in our timeline. The company may not even have ever existed in a new timeline. Or something could have happened to Wyatt's wife much earlier, and she wasn't alive to receive it. Or he could have married someone else entirely (or not have married at all) in a new timeline. Or the clerk at the telegram desk could have figured Wyatt to be another drunken fool, like hundreds he's seen over the course of doing business in Las Vegas, and pocketed Wyatt's money while throwing away a telegram that his superiors would question. Wyatt openly acknowledges from the start that he knows it's an impossibly long shot, but still has to try.
In the Watergate episode, it really should have been obvious that the doc was a person rather than a document. After all, the usage of doc as a slang for document only arose in the nineties with the ubiquity of Microsoft Word and its .doc files. In the seventies, the only meaning "doc" had was the still-current slang for doctor.
In "Space Race," the name of the fictitious aerospace company where Maria works is "Lockman," an obvious mash-up of Lockheed and Grumman. While the two firms were separate entities in 1969, it could also be that one of the Butterfly Effect changes in the timeline caused by Flynn and the team in past episodes led Lockheed and Grumman to merge before 1969.
Just as Charles Lindbergh's pro-Nazi sympathies were played up on Rittenhouse's orders in the 1930s to help foment dissension in the ranks of US society and keep FDR's anti-isolationism on the back foot, Joe McCarthy's anti-Communist witch hunt is very clearly modelled on the same lines: keeping American society preoccupied with internal divisions in order to keep attention off secret long-term plans involving circumscribing democratic and civil rights.
Henry Ford III being a Rittenhouse member and yet targeted for assassination in the Darlington 500 suggests a possible factional conflict within Rittenhouse, in which Nicholas's manifesto requires "cleansing" even Rittenhouse of members who might be insufficiently zealous toward their cause. Confirmed in "The Kennedy Curse", where Nicholas not only orders the assassination of JFK—already known to have been killed on Rittenhouse's orders—but seems to suggest that Nixon might be more amenable to the organization's aims. Nicholas appears to be attempting to actively recruit Nixon into the organization. Nixon's refusal to join Rittenhouse may have led to them having leverage over him during the Watergate affair as a result.
John F. Kennedy's embrace of civil rights in the early 1960s may well have been due to him seeing a glimpse of what racial integration could bring about in 2018, and having been armed with foreknowledge of the USA's win in World War II, would have attributed it in part to the ability of even an imperfectly democratic system to bond people together to work to its betterment.
It's been all but stated in the sixth and seventh episodes that Lucy's biological father is actually Mason's Rittenhouse contact. The implications of this are mind-blowing. In particular, if Flynn does destroy Rittenhouse, would Lucy cease to exist?
Flynn openly admits in the finale that he's aware that if Rittenhouse is destroyed, it's likely that Lucy would cease to exist. He's still willing to go through with it anyway.
Did Rittenhouse purposely sabotage Jimmy Carter's presidency? Ronald Reagan's ideological profile was far closer to Rittenhouse's stated goal of letting the elites of society amass wealth and power while presenting a facade of democracy. Perhaps even more horrifying, Rittenhouse knew about Reagan suffering from Alzheimer's disease as early as his second term—and rather than use 21st century medical intervention to help him, took advantage of the situation to more easily manipulate him. This becomes doubly horrifying in light of the fact that Rittenhouse has used modern medical technology in the past to entice people to join them, clearly implying they deliberately withheld such treatment from Reagan.
Rittenhouse's intentional stoking of nativist tendencies delayed US entry into World War II and by extension its Lend-Lease aid to the Allies. As a result the war in general and The Holocaust in particular were made much worse. The organization is beyond shadowy; it's outright evil.
Flynn sees Rittenhouse as so evil he's willing to help the Nazis and the Stalin-era USSR rather than allow Rittenhouse to win (although he does admit being utterly disgusted by having to do so).
Everything about "The Kennedy Curse". A 17-year-old boy is almost killed by his own English teacher, then kidnapped and brought to a completely alien environment by people who as far as he knows may also mean him ill. He escapes, to find himself 84 years in the future surrounded by technology he has no frame of reference for and people who think he's crazy. Once he does learn about his future, he learns of his own early death at the hands of an assassin as well as the early deaths of his brothers (and likely the forcible commitment of his older sister and the implication that his youngest brother may have killed someone as well). He then has to endure being shot at again, and having to trust his kidnappers to return home. He returns burdened with the knowledge of his own destiny. On one hand, these events may have spurred him on to a life of greatness; on the other, he's living with foreknowledge of his own death and the deaths of his loved ones. It seems unlikely that Kennedy as a result would be associated with an optimistic version of the future.