Giovanni de Medici (Dustin Hoffman's character) in reality died in his bed and WAS NOT murdered. He was 69 at the time of his death.
As Cosimo approaches the fulling mill, a man and a woman greet him as: "Master Medici". The man pronounces 'Medici' incorrectly. This mistake is extremely unlikely given the prevalence of the family.
Rinaldo degli Albizzi is shown as being of around the same age as Cosimo. However, Rindaldo was actually 19 years older than Cosimo.