That may or may not be pertinent. I see two possibilities.
1) They don't see any sign of any of the family leaving Yellowstone. They know that Lori, JJ, and Alex all left because they were seen by witnesses after that date, but since Tylee wasn't, this is the last they have evidence of her being alive anywhere. But she could have left with the rest of the family or with someone else or not at all. No way to tell.
2) They might have pictures of Lori, JJ, and Alex leaving the park, but can't see Tylee in the vehicle. That could mean she wasn't there, which means she either didn't leave or was with someone else, of potentially that she might have been in the vehicle and they couldn't tell. This possibility, while ultimately having the same possibilities of the meaning, is still a lot worse for what happened at Yellowstone. If they did find this they might not be making it public, especially since it isn't a sure thing since there is at least some small chance she was in the vehicle and couldn't be spotted in the video or pictures available.