Rockstar rewrote parts of their engine just to support the additions to the game, and want to push the open-world genre into its next step by focusing on the A.I of the various NPC characters. The game is worked on by every Rockstar studio due to the games's massive scale.
By glitching yourself there, you can see that Nuevo Paraiso is an almost 100% Shot-for-Shot Remake from the first game, with the exception of practically every man-made struture and roads, which are all missing. (Even the foliage is the same in certain locations!) This applies even to the areas that the player should never be able to see in normal gameplay, such as Diez Coronas.
Fake American: Downplayed with Arthur Morgan's voice and motion capture actor, Roger Clark, who was born in America but raised in Ireland and has a slight Irish accent.
Fake Nationality: The half-black, half-Native American Charles Smith is played by the Indian-American Noshir Dalal.
Fan Nickname: "Rootin' Tootin' Cowboy Shootin' 2" has been adopted as an affectionate nickname for the game by parts of the fandom, after the first game earned some similar nicknames.
God Never Said That: As of September 2018, Rockstar themselves has never claimed the map of the game is the largest one they've made. All claims that it is have been made by (p)reviewers, and Rockstar has actually implied that the map, while larger than in Redemption 1, is not as large as in Grand Theft Auto V by stating that they are focusing on quality over quantity and that the slower speed of the Player Character (on-foot and horse travel obviously can't beat a jet plane or a supercar) can make a smaller map look larger.
On the leaked map, Saint Denis was named New Bordeaux. The city was renamed before release after Rockstar learned that the name was already in use.
An episode of The Men from the Ministry was a story about the main duos' ancestors visiting the wild west and going against two Skinner Brothers. Considering the sheer obscurity of the show, it's very likely a coincidence.
The Other Darrin: Uncle, Javier Escuella, and Abigail Marston have their voice actors replaced from the original. Abigail's original actress does provide the character's motion capture, however.
Refitted for Sequel: The Stranger quest involving a "giant" and a midget is based on a cut stranger mission from the first game. note The original sidequest, as uncovered by modders, involved John trying to find a friend to a lonely midget. He finds a giant and persuades him to meet the other guy. However, the giant accidentally kills someone, and the little guy asks John to kill the giant. Whether or not he does would have been the player's choice.
Role Reprisal: Despite having retired from acting after the first gamenote One of only four things he'd starred in, at that, John Marstons voice actor, Rob Wiethoff, returns to continue the role hes best known for.
Time-Shifted Actor: Josh Blaylock does not reprise his role as Jack Marston, as the character is only five years old during most of the game's events and is still fairly young after the Time Skip in the epilogue. There is however a bizarre, yet seemingly a real glitch where John's (or even more rarely, Arthur's) voice changes into what sounds exactly like Josh's take on 19 year old Jack. As the lines are brand new, it's either him doing new material for future content, or it's a skilled imitator at work.
In the same interview mentioned under Internet Backdraft in the YMMV page, it's mentioned that Arthur originally had another possible love interest whose plotline was cut, removing around 5 hours of content.
Glitching into New Austin before the game opens it up reveals that Morgan was meant to visit it at some point in development, or that Rockstar simply covered all their bases. He has his own lines and journal entries for the content found exclusively in NA.