Not difficult to spot the almighty clanger here. The article is largely meaningless in terms of precision, although you can work out what they're on about - or at least assume so - if you have a fair idea of how these things work. But to the average reader of this piece, they very probably won't really know what's going on.
Anyway, it makes it sound like a car can only be plated for three years in total (irrespective of age on and off) which was to be increased to four years. Or the headline makes it sound like four-years is to be the maximum age for plated cars, whereas it's the maximum age for new or replacement cars.
But, of course, it's a three-year on rule, being increased to four-years
RCT taxis can be licensed up to four years under new taxi licensing rules
https://www.herald.wales/south-wales/rh ... ing-rules/
CHANGES to taxi licensing in Rhondda Cynon Taf (RCT) will allow taxis to be licensed for a maximum of four years rather than the current three years.
A delegated council officer decision has been made to change the current age-related policy conditions so the maximum age a hackney carriage or private hire vehicle is permitted to be licensed is extended from three years to up to four years from the date of first registration, after a request from the Unite trade union.
The reason for the request is because the cost of both new and second-hand vehicles have increased in price to the extent they are now too expensive and not affordable for the majority of the trade in RCT.
Currently, vehicles which are less than three years old have annual testing, whereas those aged three years and over have six-monthly testing.
Data shows by increasing the age to four years, the overall failure rate increases from 3.47% to 5.28% which equates to 1.81%, of which there is an increase in category A failures of 1.04%.
Category A failures involve a serious defect which presents imminent risk to the public safety and renders the vehicle unfit for continued trading with immediate suspension of vehicle licence.
But the council’s licensing team has reviewed the data and is satisfied the proposal will not have a detrimental effect on vehicle safety because the six-monthly testing for any vehicle aged over three years will continue.
The decision report also said if a vehicle shows poor maintenance and failure rates, enforcement action can be taken such as suspension or revocation of licence of the proprietor or operator.
The report said the increase in age limit will allow the trade to buy vehicles at a lower cost and will encourage more drivers into the profession who are able to buy their own vehicles as opposed to driving for operators.
The policy change comes into effect for applications for vehicles received on or after April this year.
what the category A figure is referring to at all. Presumably the 1.04% is the equivalent of the 1.81% figure but only for the category A failures, but it surely could be stated more clearly 
