During Christopher Wallace's first rap battle in 1989, a poster of the movie Juice, released in 1992, can quickly be seen in the background. Tupac Shakur would have still been in high school around that same time this took place.
A C6 Corvette Convertible is shown; a car that did not begin production until 2005. In fact, the fifth generation Chevrolet Corvette was around that time (1996), but were not released as models until 1997, the last year of his life. A fourth generation could have been used rather than a C5 or C6.
When Puffy asks Biggie when he will be going to record a new album, they are seen in an apartment with a rooftop view of New York. Judging from its position, the building they are in is the Trump World Tower, for which construction didn't begin until 1999.
In the middle of the film, when Biggie crosses the street to talk to a woman, a Ford Crown Victoria stretch taxicab with the new NYC Taxi decals is seen as well as a 2008-2009 Ford E150 or E250 Van, yet Biggie died in 1997. Stretched taxicabs weren't common until 2002 and that the new decals weren't used until mid-2007, a decade after Biggie's death.
In a brief establishing shot of Los Angeles, the Staples Center can be seen. This building did not exist during Biggie's lifetime (Biggie died in 1997; construction for the Staples Center broke ground in 1998 and opened in 1999).
In a brief establishing shot of Times Square, a billboard poster for "Chicken Run" can be seen. Chicken Run was released three years after Biggie died. There is also a poster for "Will & Grace" on NBC, which premiered the year after his death (1998).
The scene when Biggie returns to his hometown, Brooklyn; a W211 Mercedes-Benz E-Class is shown in the scene with a Corvette C6. The W211 wasn't put into production until 2003; but a W210 was around that same time this film took place.
When the young Christopher Wallace is writing rhymes in his notebook on the stoop, he is left-handed. Then when the grown up Christopher Wallace is in prison writing rhymes in his notebooks, he is seen writing right-handed.
When Biggie is free-styling, Lil Kim is first seen with her mole on the left side of her face. The mole changes sides on her face abruptly between shots; when it cuts back to Biggie rapping and back to her, it switches to the right side of her face. The next time we see Kim again, the mole is now back on the left side of her face.
When an older Biggie and D-Rock are running from the cops, you clearly see Biggie toss his gun away; however when he is cornered in the alley, the cops instruct him to put his piece down. Some would say there maybe two guns were used in the scene, but when the two are in the interrogation room - there is only one gun unless it was the same one he had dropped earlier.
Within a montage sequence of the Notorious B.I.G. becoming famous, one scene involves a group of kids listening to B.I.G; the camera crew can be briefly seen from an apartment window below from where the kids are on the left side of the screen.