maybe other ppl are more suited to answer this than me but this was the case in the maths ext 1 and 2 hscs, extra writing booklets were blank ofc, but the invigilators gave us time to fill in every page with our numbers after the exam time finished while they watched each of us (it took forever cause you had to wait till they got to you). it would be really petty if they just made it so you have to use exam time to write it cause then no way anyone finishes paper 2. its not like they're able to accept papers without correct numbering anyway.