Search can't find a post I know is there
Why a search stops where it does, and the three things that make it miss.
Read the line under the results first: it says how far back the search looked.
The post is older than your search reaches
If it says Free searches the last 7 days, the post is older than that. Paid and Premium search everything you have kept. If it says the search stopped at a date, press Keep searching to carry on further back.
The words are in the article, not the post
Search reads each post's title, summary and author, as the feed gave them. Words that are only in the article behind the link are not found. Search for a word from the title instead.
Show is set to Unread or Read
A search keeps the Show setting. Set it to All to search every post.
A word is acting as an operator
OR, AND and NOT in capitals, and a word starting with -, change what a search means. Quote them to search for them as words: "OR".
The post has left your queue
A post that aged out under its feed's span, or that you unfollowed with its feed, is no longer kept, so search cannot find it. Saved posts always stay; see Save posts.