I’m a good proofreader – I fairly reliably can open a program and book and find the one error that the publication process missed.
And yet, I am unreliable at catching typos or errors in my own writing – both words and music.
I think it’s the old problem of fresh eyes. By the time something is being locked into print, I’ve looked at it so many times that I see what I think is there, rather than what’s actually there.
It’s why book publishing comes with such a rigorous line edit, copy edit, and final proof process, with multiple sets of eyes reviewing the manuscript. And even so, no books are ever error free.
So when I spot an error in a published piece of music, or in a book I’m reading, I take it as a sign that great care was given by the creator – they spent enough time on it that they could no longer see the few remaining errors.
Errors happen, and they will continue to happen regardless of how hard we work to catch them all.