Not a single mistake! (6)
I believe the answer is:
errata
'not a single mistake' is the definition.
I can't judge whether this definition defines the answer.
'a single mistake' is the wordplay.
I cannot quite understand how this works, but
'a' is found in the answer.
'single' could be 'a' and 'a' is located in the answer.
'mistake' could be 'err' (synonyms) and 'err' is present in the answer.
A single letter 't' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for errata that I've seen before include "Boobs in a book" , "Slips" , "List of printed mistakes" , "List of text corrections to be made in a publication" , "List of printing mistakes" .)