raw denim can have any type of fabris content that any other denim can have. i have seen raw jeans with silk, linen, polyesther, and lycra in them many times. it is all in how they are dyed, not in what type of fabric is woven into the denim.
the sheer model is the only 17.5cm jean that is raw. maybe the ones you saw were a different pair in the 17.5cm cut.