I just figured out the answer to a trivial question: Does my Netflix "viewing activity" page include titles that are no longer available on Netflix?
The answer is yes. I went to my account page and scanned my viewing activity, and movies like The Pill (which was removed at the end of December) are still listed. If I follow the link, I can still view the title card, read a synopsis, and give the movie a "thumbs up" or a "thumbs down."
Another question I had is whether a title will appear more than once on the "viewing activity" page. The answer is no. I did a CTRL+F for "Civil War," and there was only one result. But I've definitely watched Captain America: Civil War multiple times.