I work for DWP, although I've never worked on the Pensions side.
20 years ago we knew the pension age would have to be increased, but perhaps I was more aware of the discussions around it because of my job role. Plus, about 14 years ago, we could see it coming into action because of the changes at which each claimant (I worked on JSA at this time) was due to reach retirement age.
I think the main unfairness is for those women born at the beginning of the 1950s who, regardless of the reasons why, were unaware of it and weren't notified.