Marked dates in wrongly (7)
I believe the answer is:
stained
'marked' is the definition.
(I've seen this before)
'dates in wrongly' is the wordplay.
'wrongly' is an anagram indicator.
'dates'+'in'='datesin'
'datesin' is an anagram of 'STAINED'.
(Other definitions for stained that I've seen before include "Church feature - side sold was wanting (anag)" , "Like many church windows" , "Marked, discoloured" , "Soiled" , "___ glass" .)