Steve:
I've got the same question about the bottom of mine, which is ground and polished also. However, it isn't an expert job as there are couple of little bevelled edges. It does have some wear, but the fact that the bottom is slightly concave means that bowl rests on a narrow edge, which has all the wear. I have a smaller yellow and white piece with the white on the outside. The white on both is pretty strong and clear for Chinese. So, I'll go back to Murano.
It's not a big deal as I've never thought of them as anything other than not too bad to look at for what we paid for them. If they're Chinese, I'll still keep it as there's a purity about it which, while it will never put in my display cases, will keep it around.
David