Interesting. Makes one wonder whether or not even Cumberbatch knows who John Harrison really is. I wonder if they filmed multiple "endings" that unveil his identity, to dilute the potential for secrecy leaks. Sort of in the same way there were several different versions of the "No, Luke, *I* am your father!" scene from Empire Strikes Back (one version of the script had Vader saying "No, Luke: Obi-Wan killed your father."... which I suppose retroactively would be sort of true).
more likely that when they film out of order and you aren't there on the days you aren't in the scene, and the special effects aren't in place it's harder to get a sense of what the finished product will be.