The Spy Game is changing
Some of this may be things that used to work, which fail badly with new methods being applied since the Cold War. Consider things such as biometric data on modern passports, which is hard to fake. And we have fingerprint sensors on some of our phones. Some Russian Spies, in the old days, managed to use more than one identity, and not every one can have been identified. We're reaching a point where the document isn't use-once, it's the human.
One thing we know is that here in the UK, we were very good at catching enemy agents and persuading them to work for us. And that depended on being very careful about revealing what we knew. It's possibly why some things were not reported to the politicians. So, through a lot of hard work, we identified two Russian agents. We stood a good chance of being able to spot them crossing a border, whatever documents they used, and that could have given away something else.
What is going on?