I have noticed on the UK 2016 5 pence that there are 2 different reverse dies used.
The first one seems to be carried over from the 2015 year issue and has a worn, flat dull finish with little detail to the background of the shield.
The second (I presume - new) version has a much sharper & shiny detail to the shield background, this also seems to be used on the 2017 issue and onwards.
Merv*** Moved by Staff to a more appropriate forum. ***