GR 323 is G (2016 in Ford parlance) R model # 323 of approx 500 made for 2016. AFAIK, no one has a definitive # on how many "street" and Rs have been built for 2016 - if anyone does, please chime in! I have seen R plates as high as 499, and street plates over 5000, but they don't use every #, and some were built and not available to the general public.
H would be 2017, F was 2015, etc.
Mike