I believe you're right Audrey but even if the prom was held on one of the earlier dates, we received no proof of Trig being born on April 18th. Maybe he was several weeks old by that date...unless there's something I missed and April 18th was confirmed as the birth date.
Per se, you have not "missed" anything. However, I have been looking at all evidence on this matter for months now. I know that many different scenarios have been proposed. In a comment within the last couple of weeks someone suggested that Trig could have been born as far back as February, though I can't remember why the person thought that was possible and actually cannot locate that comment right now.
I certainly might be proved wrong on this issue, but here's my call. I believe that someone was in labor on April 17th. Without that fact, Sarah Palin's very public, very visible, very commented on, and extremely implausible trip from Texas to Anchorage, which commenced around 2 PM (Central Time - 11 AM Alaska Time) on the 17th and ended up 12 hours later at Mat-Su Hospital in Palmer makes no sense. The only reason we really have something to talk about now is because, on April 17th, she left a conference early, changed her travel plans, got on an airplane, told people that the reason she did this was because she was in labor, and then - voila - produced a baby six hours later. If Trig Palin was already born, and "stashed" somewhere, this trip (and dramatic production of baby the next morning) makes no sense.
Was Trig Palin born
1. at 6:30 AM on April 18th
2.at Mat-Su Regional Hospital in Palmer Alaska,
3.delivered by family practice doctor Cathy Baldwin-Johnson?
I think all three of those statements could be questioned. But I believe both his birth day and time were very close to this. While I will always look at new information as it becomes available, attempts to place the birth too far outside of this time slot are a distraction at best.