It's possible most of my Yucca care and propagation knowledge came from you on this board. 2 of the plants in my Y. gloriosa grove are just branches I cut off, let dry, then placed in the ground to root. That info may have come from you. It's doubtful I would have done that if I didn't read it here maybe back in 2014. Here is where I learned that moisture and their own blooms are their biggest enemies. Thanks for all that.
I spend about 8 total hrs or maybe more per season cutting the tips off of my Y. gloriosas. I cut about 1/2 to 3/4 inches off. Y. gloriosa dagger tips don't bend if they poke you. If one wasn't careful and fell into one of these plants it could almost be deadly I'd say. That's my segway to the subspecies question...
I am not sure, but I haven't noticed more similar Yuccas anywhere. They are similar in texture, color, and appearance in general except for the curved daggers of Y. recurvifolia. I never cut the tips recurvifolia because they bend and not stab so much into you if you lean into them. They don't grow with as much vigor and speed as gloriosa and get more burned from the colder winters. For me, Y. gloriosas grow 3-4x as fast as Y. recurvifolias.