Goldenear
There can be a great deal of sonic differences between albums in the 60s and 70s. It can be due to the press run (some were in the millions), the amount of time spent in the album press (45 seconds produces an even surface), the quality of the stamper used (master tape or second generation plate), and the type of vinyl used (there were over 13 kinds of pellets used). There are numerous sites on the internet that track, grade and score albums by their quality based on serial numbers and first versus later pressings. I can reference Tom Port at Better Records who has made a living around this.