FMC and the dealer have to live in a litigious world. Most often speedos will read a bit fast so people are less likely to get nailed in speed traps. Would not be surprised if FMC likes +5%.
I make continuous process machinery (fabrics) and never will you get two 'speedometers' to agree. There are simply too many variables (underlying tech, slippage, wear, etc.) to let this happen.
Commenters have already pointed out the wheel/tire/inflation/etc. variables the MKC speedo sees.
NOTE FMC does NOT put speed on the GPS/NAV. Why? They would never agree and the Forum would be loaded with 'how come' threads. Your Waze is obviously a third technology, cell location.
I agree 5mph for your car, if police verified, is a bit high- I would expect about ~5%. I bet if you had the tires fully inflated or a different tire/wheel combo, this would drop.
That said, I would like to know another car manufacturer that can dealer tune speedos to suit every customer permutation.
You can make yourself nuts with this.
But you are very knowledgeable now about your MKCs setup and can drive accordingly.
'15 Ingot Silver/ White Sands/ Reserve 2.0 FWD/CCD/ Tow Pkg/ Oct 14 2014
'55 F-100 and 64.5 Mustang Convertible