In The Prestige why did nobody notice Fallon's deformed hand like Borden and figure out the "trick" of them being secretly twins? Is it something overlooked by the writer or is there some in-universe explaination?
At the end of the movie, once Angier figures out that Borden/Fallon were twins, they show flashbacks where the twins take the time to cut off two fingers from the "healthy" brother. It is even alluded to earlier in the movie, when Sarah (their wife) comments how the almost-healed hand has started "bleeding again".
So, a combination of black gloves with fake fingers (mentioned in the movie as well by Angier and Olivia), combined with the fact that after a few months both twins had two less fingers means that no one had a clue.