I've noticed that with some "old" hairs, their bump was somewhat weak (not sure if it's the right word or not).
If you check Ghostship's material setup, you should see a compound node: jump in and try to increase the Bump: strength parameter. In my case, I had to use 0.5.

Here, I've used one of OutofTouch Blending maps to juxtapose two colors, with the Bump distance raised to 0.5

𝒫𝒽𝓎𝓁

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