Mellylou, my 2 cents worth, …. I think you plates were made specifically as “decorator” or “collector” pieces because of the “high” rim on the backside with the holes in said. Standard plates do not have such a high rim, except “restaurant ware” may have a rim a little higher than normal. Check the inside of the holes in the rim to see if there is any glazing in them. If so, that means the holes were drilled before the glazing was “fired” on them and thus made specifically for “hanging” them on the wall.
And I wouldn’t call them “cobalt” but maybe a “royal blue”.
And Ironlord, said “unglazed rims” do not really apply to plates, cups and saucers (except “restaurant ware” again), …. but to the larger heaver items such as really older mugs, jugs and large serving pieces. Now on many pieces of old pottery and porcelain one can see “3 small dimples” on the backside. These were caused by the projections on the “spider” that was used to set them on in the kiln when “firing” the glaze.
Of course now, there are always exceptions to any "2 cent'ers".