ours was a "Marriage Certificate Shock"!
We needed a Civil Certificate for inheritance purposes several years ago (married 25 years at the time). We probably had used our Church Cert before that (issued on marriage day with correct date).
OH went into GRO, and applied - no marriage registered! Eventually, marriage was found on 1st of month, rather than 18th.
In order to change this, it seems we'd have to go to court, etc.
So now we just use the incorrect date for official purposes.
eadaoin