Tony,
There is a plausible, not outside the realm of possibility, that the difference is in the vinyl itself. I know that this concept is hard to grasp, but the record vinyl is, especially at the higher frequencies, flexing. So long as the forces are within the elastic limits of the vinyl, no permanent damage is done.
1. If you read and can understand this article -
Disc Phonograph Records by Dr. A. M. Max, RCA Engineer Magazine 1966-08-09 - 1966-08-09.pdf (worldradiohistory.com) then you may appreciate the stylus forces (>10,000 psi) that are developed during playback and that the record material is flexing/moving during playback. So, each stylus profile and VTF exerts a difference pressure which then deforms the vinyl differently depending upon its physical properties. You may not notice this on lower frequencies where the vinyl likely deforms very little, but the higher frequency side wall ridges are much more susceptible. And the physical properties are affected by the vinyl composition for which variances between pressings can change and where the pressing time & temperature can vary.
2. If you read and understand this article
Disc cutting in theory, Hugh Finnimore, Studio Sound and Broadcast Engineering, July 1975 - Studio-Sound-1975-07.pdf (worldradiohistory.com) then you may appreciate again the stylus forces that can be >1000-g’s that can be developed during playback. Any variation in the vinyl properties can affect how the stylus reproduces the groove.
3. This concept of the elasticity of the vinyl is discussed in this this article - Stylus Mass and Distortion, By J. Walton
Wireless-World-1963-04.pdf (worldradiohistory.com)
So, it's possible that the difference is the vinyl itself. I use a UV light to inspect the surface for lint/particles, and under UV light, the color and appearance of the black vinyl can vary widely, especially older records. Newer records appear to be using a new pigment that adsorbs UV light and they appear absolutely black, the book Chapter IV addresses some of the variances.
Take care,
Neil