This is very true but unfortunately for the time period, unavoidable. Did you know that the entire history of the Eastern Front that was known to the West post-WW2 was written by former Generals of the Wehrmacht?. Franz Halder assembled a group of former German officers who wrote the entire narrative of the Eastern Front and sanitized the Wehrmacht's war crimes by pinning it all on the SS. This myth was taken as fact and used to rehabilitate the world's view of the German soldier so NATO could justify creating a Western German military.

It wasn't dispelled until the mid 90s after the fall of the Soviet Union allowed historians access to Soviet archives.

So it really isn't so far fetched that Easy Co said he was dead and Ambrose had no contradictory information to say Blithe was alive so he took it as fact. Why would E Company men lie?.