Just in case you missed it, as I did the first time I saw this series: All the way back in episode one Jean and Lionel were talking in the lobby of the hotel. Once they realized that the letter was mailed but never received, they speculated on its potential whereabouts. They finally decided that the best place for it would be at the Imperial War Museum. To read a summary of their conversation in that episode go back to Season 1, Episode 1 (next to the last paragraph) in this guide. It didn't seem important then, but 46 episodes later it proves to be indeed almost a miracle.
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