In Song Settings, the mouse-hover help over "Use 4 bar ending for RealTracks" says "...Not all RealTracks have these endings yet. Check with pgmusic.com for free updates to get more".

Obviously, I can load up a style that seems appropriate, then Generate & Play, but it would be helpful if I could see which styles wouldn't produce a tidy 4-bar ending without having an extensive trial-and-error session.