Factual error: When Patrizia Reggiani signs cheques on her father's behalf, the bank that issues them is "Banca di Credito Colli Briani." Reasonably enough, is a completely made up name for a bank, but also bizarre because "Colli Briani" would be a toponym ("Briani Hills") but does not match any name in Italy - at most "Colli Briantei", which would be the Brianza region, not far from Milan where the story takes place. No other names of places or people in the rest of the movie are fictional. Moreover, the cheques don't have the number of the account they are associated with, and they are out of order. (00:03:40)
Factual error: When the Financial Police (Guardia di Finanza) arrives at Maurizio's Mansion, it should be in the late 80s, but they drive an Alfa Romeo 155. This car was produced from 1992 until 1998. (01:29:21)
Factual error: When Tom Ford reads The New York Times article about his successful show, his copy from Sunday March 13 1995 is a Frankenstein made out of different articles from different parts of the year that don't match the titles (the 'utility employees' article is actually about a single mother in a dire situation, published on December 26, the 'Soviet ship' article is from November 10). Also, there's the small detail that March 13 1995 was a Monday, not a Sunday. (02:16:35)
Factual error: During Aldo's phone call to the newlyweds, above the washing machine there's a bottle of "Omino Bianco" laundry detergent. It's an Italian brand that in the 80s was exclusively an additive bleach in powder form, the one in the movie is the modern liquid detergent version. (00:33:30)
Factual error: During the wedding scene and in other rare moments Lady Gaga and Adam Driver speak actual Italian (let's not get into the logic of the fact that they speak throughout the whole movie with 'English with Italian accent' in Italy, especially when it is pure pantomime like Leto's), but they are not native speakers, their pronunciation is off. Al Pacino does worse when in the next scene he greets the housemaid Claudia with "Buonasera" (good evening) which the captions (and the rest of the dialogue, since he repeats the line in Englishalian too) translate as "Good Morning."
Factual error: Adam Driver and Lady Gaga are eating some street food in Piazza del Duomo in Milan after trying the expensive and historic Savini restaurant. The scene begins with in frame the sign of the jewelry store Currado, a brand established in the 90s and that opened that particular store in 2007. (00:12:00)
Factual error: When Patrizia is stalking Maurizio pretending to read some law book from the university, she's leaning against a shelf that sports a grey book by the title "Formazione; I metodi." On the book, you can see the logo of the publisher, Raffaello Cortina Editore, founded in 1980. The scene is set in 1978 (the book is from 2014, incidentally, and the scene was shot at the Cortina bookstore). Another even more obviously anachronistic book is next to Maurizio on the lower shelf; about the regulations of the European Union, which didn't exist at the time. (00:08:25)
Factual error: Maurizio Gucci is killed practically in front of a recognizable landmark (Fontana delle Rane, "Frog Fountain") in Rome, but in reality he was killed in Milan. The registration plates of the cars in the scene are also "MI", which would be a pretty extraordinary coincidence in Rome.
Factual error: When Patrizia tells Maurizio that she talked to Paolo, the coffee table showcases a variety of books completely inappropriate for the 1983 timeframe (for instance there's "All Prints of Kusama Yayoi" with her pumpkin print from 2005 on the cover and "The Lives of Others" by Simon Watson, which came out in 2020). (01:16:45)
Factual error: When Patrizia gives her reluctant father-in-law the locket the birthdate of the baby is not only historically inaccurate (real life Alessandra Gucci was born in 1977, in the movie they hadn't even met by that time) but does not fit the altered timeline of the movie itself, since it says January 20th 1980. It was established that they met in 1978 and married 2 years after that, so a baby in early 1980 is way too soon considering the pregnancy happens way after the wedding in the movie too. (00:58:40)
Factual error: The scene inside the bookstore takes place in March 1978, as shown also by the calendar behind Adam Driver, which says "March 1978." But, it's not a March 1978 calendar. The Sundays (marked in red) don't match. They just took whatever calendar they had and changed the top. (00:09:40)