Complex sentence: While they admit that and (as Л) occur mainly before front and non-front vowels, respectively, they state that, at least in the prescribed norm or in some words, (as Љ) may also occur before non-front vowels.
Split into simpler sentences: While they admit that and (as Л) occur mainly before front and non-front vowels, respectively. They state that, at least in the prescribed norm or in some words, (as Љ) may also occur before non-front vowels.