If you had access to that kind of information you wouldn't want to take advantage of it in any way that might become visible, because you'd get busted.

It's like how John Walker only sold month-old crypto keys from the US Navy to the Soviet Union

https://news.usni.org/2014/09/02/john-walker-spy-ring-u-s-na...

Had the USSR been decoding US Navy messages in real time, they might have used that information, making the US Navy suspicious about how the USSR knew what it did, and causing the leak to be exposed more quickly than it was.

That's a very old intelligence conundrum. Using enough intelligence to benefit you without exposing how much ( and potentially from where) you know is a very tough problem.