Meta’s content consists of both recently published papers and older papers. When you search for papers, the default setting is All Time, which means Meta will search for the most relevant and impactful papers from all available. (The total numbers of papers related to your search is displayed above the results.)
To limit your results by time, go to the filter panel to the right the search results and select All, Last 30 Days, 90 Days, 6 months, Year, 3 Years, 5 Years, or 10 Years.
To access older papers, sort your search results by recency, then click through the pages of search results to go back in time. You can also search for older papers directly by using the paper's title.
For more information, see: How are my search results ordered?