[SiempreViernes]

Certainly for the ions lines (hugely important modelling stars for instance) you are talking about trying to measure on very hot gasses, and I've been told the problem is that it's hard to make a gas very hot while also dense enough you get detectable radiation out of it.

[amluto]

That makes sense.

Part of my point is that the authors found a temperature scale in the NIST data. One plausible source is experimental considerations: if enough of the experiments are conducted at similar temperatures, you might expect to see something related to those temperatures in the data.