I doubt we all know all of them. But they tend to persist for long periods, and so are easily discoverable by reverse engineering speeches. It helps that some people are quite explicit about it. Either in historical retrospect, as with the Atwater quote here: https://en.wikipedia.org/wiki/Southern_strategy#Evolution_.2...

Or with "saying the quiet parts loud", where people who aren't as good at dog whistling drift into being more explicit. Or people who are explicit get pushed into saying things where the racial connection is more easily denied. The Trump administration's Muslim ban is good example of that. They started out advocating for a ban with strong religious and racial components. When the public and the courts said no, they iterated to something less blatant. They will keep rinsing and repeating until something gets through.