Of course, which will mean some people will get more than they should (e.g. people who made no adjustment at all, or those who were fully aware of the change) and some will get less (people who were genuinely hardshipped because of it). I would imagine the latter will be the minority, especially if 3m people are included.
A member of my family is included, and she is just seeing any payment she might get as a pure bonus.
She had several jobs but didn't need to work for the money, her husband was the main earner and they have always been comfortable. She wasn't affected in the slightest by not receiving a letter.
Should she get compensation? I can't see what for.
Will she get it? Probably.