I highly doubt this report – but take it to GM dealer and have it checked.
GM cars do not have a 3M marking on the glass – rather it is a GM logo with a DOT spec number and underneath the DOT spec number. It also states that the glass is 70% transparency to meet federal requirements for vehicle safety.
Tinted film is not normally dealer installed as all GM cars are all ready equipped with tinted glass as standard equipment at the factory.
Adding another tinted film would not be legal so I do not think that any dealer would do that. (Another film would push it passed the 70% minimum.
The 70% minimum is for driver safety. Cars with darker than 70% can be ticketed although this is rarely enforced. Reducing below the 70% could make the film installer liable if their is an accident.
