Character mistake: Mr. Phillips is supposed to be a sophisticated and proper music teacher, but his behavior during Michael's first class seemed out of character. He didn't say anything when two students got up and danced in the front of the classroom. He told Michael that "everybody who takes music is required to play in the orchestra", but after hearing Michael play piano, Mr. Phillips (unauthorized) told him he didn't have to play in the orchestra." Also, he told Michael, "get out of here" - not professional. (00:21:43 - 00:26:42)
Character mistake: When Elwood tells his boss he is going to quit, his boss tells him he will call payroll and have them get his severance pay ready. While employees who resign do have final pay prepared (pro-rated pay, vacation pay, time owed in lieu, etc.) it would never be classified as "severance pay" if the employee resigned on their own accord. Severance pay is classified for employees who are terminated without cause, meaning no fault of their own. (00:43:10)
Suggested correction: This isn't entirely accurate, only what is most common. First, severance pay is not required by law, nor is paying for accrued PTO, so it's at the discretion of employers who can offer it to whomever they wish. An employer may offer a severance package for termination (with or without cause), retirement, or resignation. Often a severance package comes with certain conditions, such as the employee won't seek unemployment or work for a competitor, or may simply be money paid for PTOs.
Suggested correction: This never happened in the movie, Elwood didn't have a job.
Character mistake: The pilot announces that they will be flying from the 310 (California) to the 212 (New York City/Manhattan). There is no airport in Manhattan. The closest airports are JFK International and LaGuardia which are both in area code 718 (Queens).