I'm sure you're right that a "motivated enough agent" might trace a receiver but the two replies in the ham.stackexchange.com answer seem pretty clear that it's very difficult to do in the real world.

I appreciate technology may have changed but in the cold war many East Germans listened to the BBC East German service, in particular a programme called "Letters Without Signatures" [0] which relied on East Germans writing letters to the BBC . The programme ran for many years and clearly had a significant audience, I think if the Stasi had been able to detect reception they would have done so.

[0] https://www.bbc.co.uk/blogs/bbchistoryresearch/entries/9a651...