Rare terrible reservist made mistakes (6)
I believe the answer is:
errata
'mistakes' is the definition.
(an erratum is a mistake in a printed work)
'rare terrible reservist' is the wordplay.
'terrible' indicates an anagram.
'reservist' becomes 'ta' (I am not sure about this - if you are sure you should believe this answer much more).
'rare' is an anagram of 'erra'.
'erra'+'ta'='ERRATA'
'made' is the link.
Can you help me to learn more?
(Other definitions for errata that I've seen before include "mistakes in print" , "List of misprints" , "corrected mistakes" , "Mistakes in printed material" , "Text mistakes" .)