weird.
but also the sound quality does get worse at the end of the record
thats why they invented the cut that goes from inside out
so for classical radio braodcasts the sound quality gets better as it plays.

basically the grooves are closer together at the end so less sonic dynamics
that may be why yuo think the dimples are affecting the sound.

have a look at all your other records i bet you find lot's of dimples on them that you never noticed before.