There are actually multiple MIDI note number to note name conventions — different companies follow different standards. KMI follows the C3=60 paradigm (as does Ableton, Logic, MainStage, and more), while other companies follow the C4=60 paradigm (Native Instruments and others). It's even possible to run into a C5=60 standard, but that is much more rare.
If all MIDI notes appear to be an octave off, it simply means that there are two different note naming standards involved. it's only the note number that matters — the name is irrelevant.
Here is a handy chart for our note-naming convention: