You may not be able find a previously read article because articles "expire" after some amount of time determined by your news administrator (two weeks is a likely time period). If the article that you want has not expired, you may be able to find it by choosing the Show All Articles in this Newsgroup item from the Reading menu. This command will show all of the articles currently in the newsgroup, not just those that you have not yet read. You can even mark some of them as unread at this time to make them stay visible until they expire.
