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.
there are inconsistancies in all 30 plus year old things. lp's are subject to their enviroment, even if they began life in the same pressing plant.
No two records are exactly the same. All kinds of variations are possible even with records that appear to be exactly the same.

BTW, FWIW, this is less of an issue with CDs or digital in general I believe. Most CDs of a similar origin will tend to sound mostly the same assuming both are in decent condition.
Agree with the above. Differences between one pressing run and another can be dramatic. For the most part, each pressing run requires a new stamper, which introduces a variable. Further, different production engineers or plants often made their stampers from different master tapes.

Collectors spend hundreds of dollars for the most desirable pressings of their favorite LP's. Even two LP's from the same pressing run will vary, the earlier tending to fuller dynamics and greater low level detail. As the stamper wears down from each use, so do the sonics.

Unless you have electron microscopes for eyes, there's no way to tell any of this just from appearance. The information scribed in the dead wax may provide clues, depending on the record label.

An additional perspective: were these two LP's ever cleaned? If so how?

If one took two identical LP's and cleaned one really well while leaving the other uncleaned, the clean one would sound notably louder and clearer. This is true whether an LP is 30 years old or 30 minutes, though the 30 year old one will often be harder to clean effectively.
What makes it a "problem"? Both play, apparently.

How do you know? I have many of the same title but they are from different pressings, different masterings, different lots of things.

Thanks for your insight, Jaybo, Mapman, and Dougdeacon.. That's all I need to know.