When the Mexican inmates are walking up with the mop and bucket to assassinate the African-American inmate, it shows the African-American inmate wearing just a t-shirt on his bed. In the next scene, after he's set on fire, he's wearing his long sleeve button-up.
Despite the name Mexican Mafia, the character of J.D. is based on a real one-legged Caucasian member of the gang named Joe 'Pegleg' Morgan.
The lingo/street talk many of the gang members use didn't start to be used until the late '70s or early '80s.
When Santana visits a neighborhood party after his prison release, there are guests drinking generic tall boy cans of beer. Tall Boys didn't come around until a few years later and the only beer that was in "Tall Boy" form was Schlitz.
At the neighborhood party, many of the guests and gang members are wearing modern clothing and modern hairstyles that weren't in style in the early '60s.
When Santana speaks with his brother and friend sitting on the porch steps, the boys are drinking a 40 oz bottle of Schlitz. Schlitz didn't release 40 oz bottles until the early '70s.
The various gang members on the prison yard in 1962 are wearing modern hats, beanies and bandanas that gang members didn't wear in 1962.