Well, some of them were right. That has less to do with U3/U6 than it does the way data is gathered and the birth/death model they use. Actually trying to figure out how many people have full time jobs isn't a trivial task, and it's very much open to manipulation.
They probably make small methodology changes all the time.
For literally every President for the past 25 years, I've had someone breathlessly tell me "they just changed the way they calculate the unemployment rate so it doesn't look so bad!!!!!11"