On Sunday, West Virginia Public Radio’s Mountain Stage will celebrate its 25th anniversary with its 684th production, Joan Osborne, Kathy Mattea and a multilayer cake from Baltimore’s Charm City Cakes (home of the Food Channel’s Ace of Cakes). The show has presented nearly 1,700 musical artists of all genres, produced on stages around the state, in both Charleston, W.Va. and S.C., and as far afield as San Diego and Winnipeg. Traditionally, host Larry Groce invites the performers for a joint number at the end of each broadcast. (The producers also have done 39 standard-definition TV shows and nine HDTV specials.) Next year, the production goes all-digital. Full episodes are archived on the show’s site, www.mountainstage.org, and segments are streamed on NPR Music.