Is it ok to sing in octaves beyond the range of given examples? Some basses, for example, may be better and more comfortable down at the D# below the stave than up at the C# above the stave. Likewise there may be sopranos who are better at one octave above written pitch. Besides fitting the comfort and vocal quality of some singers, this could arguably contribute positively to the evocation of the expanse of space - just think of the 7-octave A at the beginning of Mahler 1 for example!