Nice plots!
I think 500 angstroms would be really thin for crt use. If I remember correctly 800-1500 was used for lower voltage crts (10kv or so-early monochrome) and 3000-4000 for higher voltage color types. It would not surprise me to find 5000 or so in those 30-40kV projection tubes. Argon would be another likely residual gas, as it is not pumped by barium getters.
jr