I neglected to consider their accumulated lifetime memory of how things sounded to them.
This is a powerful realization. Yes, there are certain frequencies which are gone, even by mid forties. But listening is different than hearing because listening involves attention and interpretation. There's a reason that we attend to what older scientists, physicians, chefs, etc. say about their area of expertise — because they have developed intelligence and habits which yield good judgment.
The same applies to experienced listeners, regardless of their physical hearing loss, as long as it's not dramatic or if it bears upon the very aspect of sound which is under analysis at the moment.