And this was some finale.
Actually, the whole record-breaking performance was special. Director Michael Bennett not only brought in actors from different companies who would switch back-and-forth in their roles, but the entire original cast (with one missing exception, Pamela Blair) appeared in the "names" part of the show, and several actress who played the role of 'Cassie' joined the original in the role, Donna McKechnie.
There were other treats, including multiple actors in other roles, and international casts represented by performing parts of the show in different languages.
All of which lead up to this spectacular finale, with over 300 former cast members joining the current case for the finale...ironically titled, "One."