Thanks Midazolam & BobbyCollins ... don't know where my brain was for a while, particularly as I had all the other elements & no doubt about the overall theme.
I was also very happy with my six letter word (something else which should have nudged me in the right direction at the end)
I can see where your confusion arose M ... you are reading 'correct' as meaning correct grid entry. However, it seems that what is intended is 'correct' meaning the original letter before the enforced misprint.
Perhaps it would have been clearer if Schadenfreude had said 'originally correct' or even 'replaced'