I too have a D80. Mine is serial #468671. That means both of our D80s are 1968-69 season models. You can tell yours was made after at least June of 1968 going by the lack of an "A" before the sequence number, which was used to denote D80s made in the 1967-68 season. But as to finding out the exact months of the year built, that's going to be a tough one for both of us. Good luck!
Thank to the two guys who have already posted about this Model of Kirby. I finally know that my Kirby is a D80 and had a shiny chrome finish. My D80 is SN-110468, but I don't know of a sequence number. I could only find that SN on the bottom of the motor. I'm trying to get a bag conversion kit going for my D80 so I can use it more. David in Austin