Previously, Twitter search results displayed Tweets going back about a week. We’ve developed a way to include older Tweets, so you can see content that goes beyond the more recent Tweets.
As we roll this out over the coming days, the Tweets that you’ll see in search results represent a fairly small percentage of total Tweets ever sent. We look at a variety of types of engagement, like favorites, retweets and clicks, to determine which Tweets to show. We’ll be steadily increasing this percentage over time, and ultimately, aim to surface the best content for your query.Twitter Rolling Out Older Tweets In Search Results [blog.twitter.com]