It sounds like you are in Jefferson County or Fayette County. If it has to be inspected by a Kentucky Building Inspector, yes you definitely should use both codes. And, where ever there is a conflict, go with the Kentucky Update.
I am a Kentucky Master Plumber and I know first-hand, they don't want to hear anything but the code book. Their position is, you may not be the only one to live in that house; the average turnover time on a house is 5-1/2 years. So, they are protecting the future owners as well as you.