Normally a retcon involves changing the past to reflect changes in the future of the cannon. A characters history can change at the stroke of a pen.
In the Thursday Next books, the opposite happens. The series involves characters travelling into books and being able to change them. In "One of our Thursday's is missing" events in the past are slightly different to first 4 books (ie, a retcon). However, this is changed by the events of the book so that in the end continuity is restored!
This probably makes more sense to people who have read the books, but I was wondering if there were any prior examples of the reverse ret-con?
An analogy would be a time-travel series where in a later book/episode the past history is retconned to be different, but by the end of the series history gets changed to match the old timeline.