No real change in the guidance
If you go to the Kelvedon Hatch nuclear bunker in Essex (UK) you can see the 1950s guidance for citizens.It's about as effective as this new stuff. I have a strong suspicion that for the entire history of the problem the primary purpose has been [a] to minimise an assumed public panic and [b] to minimise the proportion of casualties needing medical attention. For example, it was then recommended that you could build a shelter in your lounge by removing the door and making a tent to hide under out of it and the back of your settee.