I can count the number of days I've played bassoon and oboe in my classes on both hands combined, and I've been in the classroom twenty years. Does that mean I can't look up the fingerings when I need them? Does that mean I don't teach those instruments? Or does it mean that I can't use the resources I have with me while I'm teaching?
Bet if you ask a typical non-horn player for six fingerings for above-the-staff G, they can't do it - but there are at *least* that many. Doesn't mean they won't be a quality teacher for not knowing a second, third, fourth, or fifth alternate fingering.