Like you say,If they do have engineering department what do they do all this time. prehaps their is just one lonely engineer their with his Cad system trying to finish the new kirby for the past 20 years, almost his working lifes work.
It doesn't take 12 years to change the colour of a bag and trim.
with rapid prototyping and other new design aids designing a new vacuum would take weeks ( if not complicated ) to a few months. the most time consuming part of any design process is the development testing to make sure it works as it should and lasts as it should.
I have to wonder if they dont employ a outside design house to do a new model, like they used to in times gone by. it doesn't make sense for kirby to have a huge design department when their design progression is so slow