I think a little of both. There may be some sonic deterioration on later pressings, but I think some of it IS collectibility.
However, in digging through lots of flea markets and garage sales, I DID notice some differences on Mercury Living Presence stampings of the same LP. Noticed it 3 different times. A little more noise, and slightly less dynamics, so it seems. I always cleaned my records with a VPI 16.5, so I tried to eliminate the "dirt" difference.
Never had enough RCA's to really test this out. I just assumed it might be the same; pressing master wears out over time.....
However, in digging through lots of flea markets and garage sales, I DID notice some differences on Mercury Living Presence stampings of the same LP. Noticed it 3 different times. A little more noise, and slightly less dynamics, so it seems. I always cleaned my records with a VPI 16.5, so I tried to eliminate the "dirt" difference.
Never had enough RCA's to really test this out. I just assumed it might be the same; pressing master wears out over time.....