Instead of commenting on an answer to an unrelated question, I'm creating a new question.
Q: How many entries out of all from the contest went into HNQ?
A: Sadly the new event that shows when a question hit the HNQ is not yet implemented in the StackExchange Data Explorer as far as can tell, judging by this comment from an SE employee. Even if it was this data was only made available during the contest. So you could possibly find out about a lot of them by manually checking every question that was submitted.
And the relevant comment stream is about checking the timeline of a post, which isn't something we can actually do, as far as I can tell. The alternative is to check the edit history of a post. But it's not always there and not all posts have an edit history.
Case in point: My question Writing in a Christian voice
This was a HNQ for a day or two. I know because I checked the sidebar and looked for what was on Writing and saw my post.
I've never edited that post and neither has anyone else, so there is no edit history. I have no clue how to get to a timeline. And there appears to be no other method.
How can you find out if a question was a HNQ at some point in its history?