Act IV has always been controversial in every SL stage through the years. I've seen several versions of it, and frankly, for the modern public, way far from the XIX Century Russian one used to a very different and early technique, it's kinda hard to endure a full length IV act in the way Petipa intended. In her version for the Ballet Nacional de Cuba, Alonso has three acts plus a condensed epilogue, which uses some of the '77 music of the last act. According to her account she had observed how in some Havana productions from the past-(Mary Skeaping's)-people wouldn't stand in the theatre for the IV act, giving that the last piece of bravura_(the Black Swan PDD)-was over. The public would just leave during the III intermezzo, so she came out with the idea of a brief ending after the ballroom scene-(without intermezzo, hence kind of forcing the audience to stay)-, in which the backdrops would quickly change in the back, in the dark, while Sigfried would rush his way to the lake to look for Odette-(to the so-called "storm music"). Lights back on, lakeside, Odette/Siegfriend/Rothbart, the fight...and done deal, finito, your hands still warm after the Odile's fouettes clapping while you indulge in the vision of the two lovers reunited in the final apotheosis.