The vehicle registration date is asking the date the vehicle was first registered, this is usually made obvious by the vehicle registration number, unless it is on a private plate.
For example:
XX01 XXX=2001
XX02 XXX=2002
XX03 XXX=2003
XX15 XXX= 2015
Sometimes you will see registrations have a number in the 50's, 60's or 70's.
This means:
XX51 XXX= 2001
XX61 XXX= 2011
XX71 XXX= 2021
Usually the vehicle year of manufacture pulls through automatically with the registration search, but it is important to double check with the customer if their registration plate is private or customized.