I think it's normal for all dogs to have spots. If you shave a dog, most will have grey spots all over their skin. My corgi pup is 1 1/2 y/o and she still has grey spots upon her belly which she's had since she was 3 months old. Our other male corgi who is 3 yrs old has grey spots upon his belly as well. So they probably won't go away, they just get covered up by belly hairs when they grow older. <3
My Muffin's grey spots appeared around 8 to 12 mos. I was alarmed at first and thought she had a huge bruise/. I racked my brain to think of how she could have gotten it. now she has them on both sides of her belly. They are here to stay.