Using blue light with peroxide may be considered restoration in theory, but as I understand it, it's only detectable if someone messes up and blisters the paper—so there are presumably many, many blue-label books out there that have had this treatment.
Blue light is also being used without peroxide, i.e., blue light only. I don't believe that that is detectable at all. If it's used on non-white areas, it will cause fading, but CGC can't detect fading, anyway (unless it's severe). I don't think that CGC has ever claimed to be able to detect light-only whitening.