Mistakes have been corrected before, but certain things though pointed out, still remain the same. Other things were pointed to as timeline flux, which would make sense too.
Is there a list of previous corrections in subsequent editions somewhere? That'd be interesting to read.
I don't think that we can use dialogue as an example; that's just difference in word choice, and they're synonymous terms. The sign changing is concrete, though. It was messed up badly in Cold Days during the fight with He Who Walks Before, and was likely replaced. I don't recall damage to it in previous books that would explain it, though.
Small inconsistencies like the exact wording can be explained by this being Harry's recollections, looking back years after everything had happened. I'm not sure this is a firm example of timeline changes. However, the sign is specifically different in Proven Guilty and White Night, the two books with the most time travel theorizing; they're the same as Death Masks, which doesn't have anything to do with time travel, as far as I'm aware on my theory readings.
Heh. Maybe Harry went back to switch out the Shroud to give it to Hades, which is why it isn't the real one.