Endless Abba it turned out? (7,4)
I believe the answer is:
tribute band
'endless abba it turned out?' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'endless abba it turned out?' is the wordplay.
'endless' means to remove the last letter.
'out?' is an anagram indicator (out can mean wrong or inaccurate).
'abba' with its final letter taken away is 'abb'.
'abb'+'it'+'turned'='abbitturned'
'abbitturned' anagrammed gives 'TRIBUTE BAND'.
(Another definition for tribute band that I've seen is " Group after another".)