I happened to notice that Christina Applegate was the guest last night on Chelsey Lately, so I watched, hoping they'd talk about their WDYTUA experiences, and they did. Chelsey said hers was awful and then quickly amended that to add that the experience itself was worthwhile and she was glad she did it, but that it was awful to have to hear about some of the hardships/difficulties that her relatives went through. When she said that she thought Christina's was really moving, Christina said they actually didn't show a lot of things that she found out that were even more terrible--like that her great-great grandfather shot his brother twenty times, killing him, in front of assembled relatives. Or that her father's mother's sister died in her twenties of malnutrition. She said every time the researchers came up with another horrible story, she would think, "Really? Really? Again?"
So, apparently, though they tend to edit toward one story, the stars involved may be finding out a lot of things we never hear about when we watch the show.