The two albums used a different lacquers and the lath volume was set differently. Big pressing plants use to have multiple presses running and stampers are replaced frequently. The plant would produce multiple Lacquers to supply enough stampers to do the job. In this day and age nobody produces that kind of volume. The plants are much smaller.
Vinyl records
I have two identical LP's from 1977 in excellent condition, but one plays noticeably louder then the other. Are these inconsistencies pretty common with older vinyl records? I've been into vinyl since 1969, but have never owned two identical LP's until today, so I've never noticed this problem in the past.