I think (emphasis added since the diagrams I have aren't good enough to tell how the windings are stacked) that is possible to have 1 speed and not the other. There are certainly 2 relays in the IRCM box; one for low and 1 for high, and there are 2 sets of windings in the fan motor. However, I recall someone posting long ago, that the 2 windings were not supposed to both be energized at the same time.. In other words, one or the other is on.
You can of course, check the winding resistances yourself. Thats simple enough to do.