Always fun and illuminating! A curious mention, that they were partway through cryptographic analysis when they discovered the key in a know set of keys from t

Always fun and illuminating! A curious mention, that they were partway through cryptographic analysis when they discovered the key in a know set of keys from that time. Why not try all of those first? What was this letter even considered unsolved? Anyway, a great use for the internet, crowd-sourcing history!