The practice of severing the ring finger for assassin initiates was discontinued by Altair, the master of the Brotherhood, sometime after its reformation in 1192. This was referenced in the video game Assassin's Creed II (2009), occurring decades before the events in the movie. As the movie and its sequels are original stories set within the same universe as the games, removing a finger to use the hidden blade has not been necessary for centuries by the time Aguilar joins the Brotherhood. Ubisoft and the Assassin's Creed franchise team explained that the Spanish branch of the Brotherhood to which Aguilar belongs still severs one finger per initiate to ensure the commitment and loyalty of each initiate to defend both the Brotherhood and the Creed. This is why Aguilar has the ring finger severed on only one hand despite wielding two hidden blades; the severance is no longer about function, but rather about symbolism and dedication.
Columbus' remains were moved several times, even possibly over the Atlantic to Cuba (and back). Set of his remains are even thought to reside in the Dominican republic. Given these considerations it's premature to think they know where the apple is based on the assumption that Columbus took it to his grave.
The apple is supposedly based on the Bible's forbidden fruit, but it does not resemble an edible fruit but a human-made artifact. It is also never explained why this biblical item exists outside paradise.
When Aguilar de Nerha gives the Apple of Eden to Christopher Columbus, Christopher says: "following the light of the sun I should leave this old world behind." But at that time, Christopher didn't know that a "New World" existed, for he was just trying to find a more profitable route to Asia. If there wasn't a New World, he could not have the idea of an Old World neither.
An early scene takes place in 1986, but the cars in those scenes look too modern. For example, the SUV shown prominently is a 1997 Mercedes-Benz G-Class.
In the opening sequences exploring Cal's background before being taken to Abstergo - Madrid, (time code- 8.34, text reads "30 years later") the text that reads "Huntsville Department of Criminal Justice, Texas USA" is incorrect. This is not the geographical location for Huntsville, Texas. The Prison facility appears to be a representation of the Texas Department of Criminal Justice, Huntsville Unit. This is due to the notable inclusion of the solid wall surrounding the facility as well as the construction of several of the buildings inside the compound. The Huntsville Unit is also home to the state death chamber and houses death row offenders just prior to their execution. However, the Huntsville Unit (a.k.a. The Walls) is actually constructed of red brick and was opened around 1850 so it an older looking facility. The unit is also located in the center of the downtown area of Huntsville, TX. This city is located approximately 70 miles north of Houston, TX and is home to Sam Houston State University as well as 5 prison facilities located within its city limits.
When Cal is in the Animus towards the end of the movie, Sofia asks where he is. The lab technician replies that it looks like a military port and adds "Cádiz, Palos de la Frontera".
Palos de la Frontera is in Huelva (also in Andalusia), not in Cádiz.