Yes, that’s a problem. Working from the other direction… one of the big things about General MIDI is that if you want to write a song, you know which sounds are available so you can compose a GM track and then take it to some nicer gear and fine-tune it there. Maybe you write your track on a MT-32 or SC-88 at home, and then bring the MIDI file into a studio where they’ve got a JV-1080. Your music won’t be balanced, but it will at least be intelligible, with the correct instruments playing in the correct octave.