I didn't notice for the longest time that each had different spots. I am not sure when I finally realized it, but I facepalmed myself when I did.
Even though I notice it now, I normally just catch whichever one I come across first. I think that strangest one I have ever caught had no spots O_o
But I am not sure if I have seen the same one twice because for the longest time I thought they were all the same.