I'm too young to remember when To Tell the Truth premiered. I did grow up with it, though.
I can just remember the end of its original network run, and I turned on the Garry Moore-hosted syndicated version from time to time all through my childhood. When I grew up, and the show was revived a few times, I still made sure to catch it once in a while.
And Kitty Carlisle appeared on every one of those series at least once.

In those early years, like most other kids, I didn't appreciate what made a classy, erudite person interesting. So to me, Kitty Carlisle was just some old lady on the TV. That's not completely true, of course. You couldn't watch Kitty Carlisle without developing some affection for her. But I certainly didn't appreciate what made her interesting.

Then, I got older and began to develop wider interests. Like a lot of young people in the '70s, I developed an interest in the Marx Brothers. So, when I saw A Night at the Opera, I took note of who was playing the romantic interest. Hey, Look! That's Kitty Carlisle. I never knew she was in movies. And look, she sings!

I lived north of New York City in those years, and went to college in Albany. I didn't go to cultural events often, but I did once in a while, and noticed that Kitty Carlisle Hart was in charge of the state Arts Council. Wow, she's everywhere!
Then I got even older, and saw her pop up on every documentary you could find about Broadway. She had been married to the playwright Moss Hart (who I also came to appreciate when I got older), and she had some wonderful stories about the heyday of Broadway.

But mostly, what I remember are those years on To Tell the Truth. It was reassuring somehow, even into the 1990s and 2000s, to see Mrs. Hart dutifully appearing on each incarnation of the show.
In her single appearance on the 2000-2002 series, she was treated like visiting royalty. When the other panelists began getting a little bawdy, in a way that would never have happened in the old days, Paula Poundstone shushed the other panelists, saying "Guys! -- Kitty Carlisle is here!"

So, we have a bit less class in the world, with Kitty Carlisle Hart gone.
I'd like to think that right now, she's at a very enjoyable cocktail party with Moss Hart.