Times have moved on since then...
Would leave it to older minds who could tell you when the switch happened, but number plates now just have 2 numbers (not a bunch). The 2 digits indicate the year and half of year the car was bought. A 13 plate (i.e. SN13 KPO) indicates the car was registered in the first half of 2013, as opposed to a 63 plate, which indicates the car was registered in the 2nd half of 2013. 0X/5X, 1X/6X and 2X/7X (where X is 0-9) since the 2000s.
Actually, having just read up, the new system started 2nd half of 2001 after they used up Y-reg cars. And would have to correct "in your day" as G reg actually is from August '68 to July '69

The August to July registrations appear to have started in August '67, until which A-E were from the 1st of the year.