You could probably tell us more then most when it comes to the difference between 1st and 2nd generation that is where my knowledge becomes a little blurry
But what I understand is 1st generation is pre WW2 and 2nd generation is post WW2 up until they stopped production
3rd Generation were the "Blanks" 3.5 was the Single Man and 4th Generation is the new production...
Perhaps your books show more ???