[SiempreViernes]

> I wouldn't necessarily expect there to be any clear trend to the set of all spectral lines

Me neither, but admittedly mainly because I've never even considered the question.

Some reflection gives me the expectation that there should be fewer high frequency lines due to conservation of energy, and very many low frequency lines.

Then I imagine experimental limitations mean it's very hard to see all the low frequency transitions, but honestly I have no idea how the cross sections of the transitions go with energy so I should stop speculating.