@MartinR Thanks for the feedback. I have checked and indeed I couldn't find it in the corpus used to generate the index version currently online.

So it is not the search engine but the crawler missed that post.

However, because the corpus which I generated last year is older than the index, it is very likely that post newer than the corpus. Although the index is generated 6 months old, it is still using the corpus from the end of last year. Correct me if you find posts newer than Jan, I may forget I have added some posts after this year.