Bajazet is a pastiche. Here we find some original Vivaldi music and some used previously in is other Operas such as Motezuma or L'Olimpiade. This blend of music is used, as corrent pratice at the time, for the "positive" caracters. But that's not all!, there is some music by other composers as well such as Giacomelli or Hasse wich is used for the "negative" caracters.
I assisted the concert (with the same ochestra but another cast of singers), and, when Manuela Custer sings "Qual guerriero in campo armato" (area from Irene), the place bursts with applause. This is just to give an idea of the great music included here. It is a joy to hear from the beguining to the end, thanks to Vivaldi and, of course Fabio Biondi, who had the work to make the reconstruction of the score, this is a night i will never forget and a very rewarding listening experience for everyone.