Unfortunately I have been thrown out of stories in this unpleasant way several times now. It's not so bad if it happens early in a story, then I take it as an indicator that I probably won't like the rest and move on. But I've had it happen in stories in which the older Spock only appeared later on, and I was already invested in a longer story. Granted, those weren't masterpieces, but still decent enough, and I was like several thousand words into the events and wanted to know what happened, and then the other Spock appeared and I ran into this brick wall.