Final answer:
To find the model year of a vehicle, checking the vehicle's registration documents is the most reliable method, followed by decoding the VIN.
Step-by-step explanation:
The most reliable method to find the model year of a vehicle is to check the vehicle's registration documents. These documents are issued by government authorities and should accurately reflect the vehicle's model year. Alternatively, you can decode the vehicle identification number (VIN), which contains information about the model year, typically represented by the 10th character in the sequence. Contacting the manufacturer and checking the owner's manual could also provide this information but are less direct methods.