I have never seen a deduction for this, I thought this was just a joke in stick it, like it was a deduction in your code but nobody ever took the deduction.
I just had a look at our code of points to clarify. No where is any sort of deduction mentioned for underwear showing.
The backs of our leotards can be no lower than the lower line of the shoulder blades, but even then you never see them that low. Gyms don’t try to push the envelope with cut away backs and mesh bits or anything like that. We just have high back leos on everyone.
I think this may also be reflective in the US changing their comp leotards all the time. I am always shocked when I hear of gyms having a Leotard for two years and then changing it.
Here we have to have Leotard colours and designed registered so no two gyms look the same and everyone keeps the same Leotard for many, many years. It becomes distinctive to their gym, so that each club is quickly and easily recognised at competitions.