I don't understand your point here. He lost the cypher itself, not an encrypted message. So the code breakers would have said: yep, that's a cypher alright, it

I don't understand your point here. He lost the cypher itself, not an encrypted message. So the code breakers would have said: yep, that's a cypher alright, it can be used for anything by anyone. Being at war, you want to make sure it's not an enemy using the code.