A mistake, or did I miss something?

Rating: Null/10 (18 July 2013)

When David and the blonde guy are trying to figure out what's happening and are studying the book, the blonde guy says that 'Satan' needs to capture five souls, and then it will rain blood and a creature will rise from hell. Towards the end of the movie, when Mia is picking up her necklace after David shot the gas canister, it begins to rain blood. As I recall, the two women, and the blonde guy end up possessed. David is never possessed. And Mia had been, but David had freed her soul. So TECHNICALLY speaking, only three souls were captured. David died with his soul intact, and Mia's soul was freed. So how is it that the "prophecy" or whatever came true? So, is this a fluke in the plot? Or did I just miss something or misunderstand?