China or porcelain products will have some individuality. They are made from clay that starts wet and then dries.
There is shrinkage involved and even coming from a mold, every piece may shrink differently.
The big question is, how much is too much.
Years ago I gave up caring if the holes were just right in lavs.
As a plumber, you try to square everything up so that everything is centered, but it's not always easy.
Some of this comes down to how much it would cost to produce clay vessels that attain some sort of perfection at an assembly cost that people would still pay for.
There is always, "it's just a toilet, it's just a lav basin, I don't want to spend my kids inheritance on them."
To make matters worse, now I'm wearing bi-focals and it's even harder to tell when things are straight, everything seems curved now.
On the lav pedastal, dipping 1/8" doesn't seem like much, you will be caulking the lav to the wall. Once the faucet is on, the mirror is attached to the wall, and various things put on the lav, who's going to notice.
Sometimes, it is what it is. A hand made clay vessel with it's own individual attributes.