Complex sentence: Namkha'i holds that Vairotsana codified this work from oral instruction by Padmasambhava though Sri Singha a student of Padmasambhava and also a teacher of Vairotsana spent considerable time in what is now known as China.
Split into simpler sentences: Namkha'i holds that Vairotsana codified this work from oral instruction by Padmasambhava. That said, Sri Singha a student of Padmasambhava and also a teacher of Vairotsana spent considerable time in what is now known as China.