I notice that one of the pieces of info that the first PDF asks for is a VIN#, which is a standard format 17-digit serial number
17-digit serial numbers are standard for newer vehicles. However, many older vehicles had less than 17. I have an antique motorcycle with 6 digits. MA titled it no problem with only the 6. Your serial number is your VIN, so you must list it on the application exactly as it appears on the car/motorcycle/moped. Do not add extra digits.
Hope this helps.