Interesting read, Simon.
If I remembered right, criminal psychology assumes that it's impossible for genuinely guilty perpetrators to consistently tell a lie. While some minor details might be left out, the narrative shouldn't shift dramatically. So, it's like you say, 'the gist stays the same'. But suspects aren't actually convicted because they missed the details. Rather, they're convicted because the 'gist' didn't stay the same.
Is it really true that genuine memory gets fuzzier each time one recalls and recites it? Isn't it more intuitive that the memory gets clearer and more opaque?