Cab Headliner Replacement

[Oldman]

I've seen many buses with the same staining on the headliner including my own, hence the observation.
I'm not convinced that it's nicotine/smoke related as the staining is more prominent on the lower edges of the liner itself....where the lower edge is captured.
Looking at your pics it seems possible that the staining could be surface rust related from the retaining clips themselves....?

One trick I was told was to warm up the headliner with a heat gun as you stretch & capture the edges....once the material cools, it shrinks slightly helping prevent any annoying ripples....