Why wasn't this question automatically protected after the third answer from a new user?

Question

This question received its fourth deleted answer from a new user just a few hours ago. It was only at that time that the question was automatically protected. However, according to the FAQ, questions are automatically protected after receiving just three deleted answers from new users.

Why wasn't this question protected upon the third deleted answer? All of the deleted answers are from different users, and while the question was migrated from Stack Overflow, all of the deleted answers were posted long after the migration.

I can think of three possible causes:

1. One of the older new user answers was posted by a user with the association bonus, so it's possible that it wasn't considered towards the check as it only checks for 10+ rep, without subtracting 100 for users with the bonus like the answering check does.
2. One of the deleted answers was deleted in review, and since that didn't generate a deletion revision history item in the past (thus allowing for the author to undelete it), it may not be being counted.
3. Two of the deleted answers were self-deleted, and self-deleted answers may be exempt. (Not possible, since if it were the case, it wouldn't have been auto-protected until the next deleted new-user answer.)

I'm leaning towards cause 1, but which one is it, or is it something totally different? Is it easy to fix?

Answer 1

It's #1. Users with the association bonus are not considered new users, because the association bonus explicitly exists to bypass that and other reputation thresholds. The only exception to that rule is being able to post to protected questions.

One thing of note is that there is no "WasNewWhenPosted" flag of any kind that gets added to answers. That user likely didn't have the association bonus when it was posted because that's when they first started contributing on the network. But the system doesn't keep track of if they posted it before or after they gained the reputation. So gaining reputation on the site subsequently makes the answer ineligible to trigger auto-protection in the future if it hasn't already been triggered.