In general, you only need to view the Event Still once. The events are listed below in order of their appearance on the View Event Stills page. This post is my attempt to catalog all the event stills and how to obtain them in game. However, there has not been a very good guide as to how to achieve all 30 events, especially with problematic and rare ones like Secret Meeting. It’s one of the things required for One Hundred Percent Completion of the game.
Upon collecting all 30 and winning any scenario to unite China, you will unlock top-tier skill sets and all historical portraits when you use Create Officer for your own custom officers. In Koei’s Romance of the Three Kingdoms XI for Windows PC (non PUK, English edition), there are a total of 30 event stills ( basically, pictures of important events during a campaign, viewable under Settings -> Reference -> View Event Stills ).