Fridge Logic: Who exactly was that corpse in the Norwegian camp?
One possible explanation brings this into Fridge Horror territory: it was a Thing, acting dead in the hopes of infecting an unsuspecting isolated victim.
Fridge Brilliance: There's a few grammatical errors throughout Irina's Memoir, such as Yuri shouting "Someone help me with this man" when he was restraining Kate. At first they are somewhat annoying... except Irina couldn't speak English, so she presumably wrote her account in Russian and had it translated.
Harsher in Hindsight: In Irina's Memoir, Irina hints at her lesbianism and talks about how she kept a photo of her lover hidden because she didn't want anyone to find out. It makes sense considering this is 1982, when Gay Rights was still a very difficult subject. However, Hitchcock might not have included that element if he had known that roughly a year later Russia would pass a law against homosexuality.