Oh that's ok then Cruiser
I'm really good with figures and calculations but you really do need a quiet spot and a whole day for some of those gmp ones. The trouble is they've changed a lot of times, and so if you've worked a normal length of time you come under about 6 different sets of regulations, and the gmp has to be calculated for each - manually - for each year of work, divided by 365 and multiplied by how many days of that tax year you worked under that regulation. Then another set of regulations applies as to how much is from each set...oh and almost each one increases by a different percentage each year, but if increase x is less than increase y, then ummm, something happens
The original calculation would no doubt have been double or triple-checked, by different people, but it is understandable that every now and then something is wrong.
It wouldn't really be anything much on the actual 'main' part of anyone's pension, but the gmp bit, yes, it's more than a nightmare