Sure, that they pre-tape is no secret. They usually post 'recorded earlier' when that happens and I was even there for one, last year. But if you've going to pre-tape a week or two of shows, AND pre-tape her 'last day,' why not play her last-day tape...LAST?
Ah, well. Television.
"There is no use trying," said Alice; "one can't believe impossible things." "I dare say you haven't had the practice," said the Queen. "When I was your age, I always did it for half an hour a day. Why, sometimes I've believed as many as six impossible things before breakfast." --Alice in Wonderland