I could hear the 14kHz clearly, which surprised me a little, as last time I tested it my limit was barely 12kHz. (When I joined the BBC at age 23, they measured my limit as 17kHz.)
What I did notice is that even on bloody good headphones through an excellent interface there were clear artefacts audible to me on every higher signal. In some cases these even sounded like a tone,
but not the right one (which presumably would have been louder if I could have heard it); but this possibly means that some care may be required to choose the right answer.
I'm interested by the number of people claiming to hear appreciably over 20kHz. In my experience this is really unusual for people of age 20 or more. I have been led to believe that there may be a correlation with suffering from asthma (indeed, the person I knew who could hear highest as a student - 23kHz - not merely suffered from asthma, but died as a result of an asthma attack at the age of 50).
It's possible for people to lose specific frequencies or ranges of frequencies in their ears, and not necessarily in order of highest to lowest. Which would explain being able to hear all of them but 19 kHz.
But that's also true to some extent of headphones or speakers...