When we measure absorption/emission spectra for hydrogen-like atoms, we can point to a particular line/energy level and say "Aha! That's almost exactly the $A\rightarrow B$ transition that we predicted, so we have good reason to hereby label that spectral line the line that corresponds to the $A\rightarrow B$ transition."
How is this done for complex multi-electron atoms? Are specific transitions between resonant states able to be predicted/calculated for such complicated systems? I would imagine that even the notion of electron orbitals (in terms of those for the hydrogen atom) would get mixed up for more complicated atoms.