Of them are long gone and were a part of that specific time period? Pardon me if that sounds confusing , but its hard to explain

Kind of. For example, I love the Little House books and when I read about a party they had or something like that I go and realize all are long dead and so are their kids, even grandkids. Some might have distant relatives alive but they weren't alive more than likely to have met the people in the books.

This happens when I'm watching an old film or TV show. While watching, I realize most of the cast is dead and that they aren't here any more. That they lived through a specific time period and is now gone