What is your year tire size? is it the stock 180/70 or has the PO changed it to either the 200/70 or the 170/80? Either of these will make the speedo read pretty much accurately. Or if they changed out the stock drive pulley(s) with the aftermarket overdrive pulley(s) that also corrects the speedo.
Or the Harley could also be off as are a lot of motorcycles. The best way to find out is with a GPS. First time i had my 9 or the highway I was doing what i thought was 120, but was not passing many people, Not even the school buses.
From what I know the bike is stock but I'll check these things out. For almost $30,000 out the door you'd hope the Harley has an accurate speedo! I will try with GPS when I can as well...