Imagine there is an electron-stripped nucleus with $Z$ protons, in high vacuum and isolated. Then you add electrons, one by one, and check which orbitals are filled. Will this depend on $Z$ at all, or does it only depend on the number of electrons that are added?
In other words, will an ion have different orbits filled than the corresponding neutral atom with the same number of electrons?
In other words: are there atoms with numbers of protons $Z_1$ and $Z_2$, both with $n\leq\operatorname{min}(Z_1, Z_2)$ electrons that have different orbital fillings?