In the United Kingdom, number plates change twice a year. The first series of number plates are released in March, and the second series is released in September. The format of the number plate indicates the year of release.
The “66” number plate you are referring to would have been released in September 2016. This is because the number “66” corresponds to the second series released in September 2016. The next similar number plate series would be “67” in September 2017, “68” in September 2018, and so on.