Declared a number were incorrect (7)
I believe the answer is:
averred
'declared' is the definition.
(averring is a kind of declaring)
'a number were incorrect' is the wordplay.
'number' becomes 'v' (V is an example).
'were incorrect' becomes 'erred' ('err' can be a synonym of 'be incorrect').
'a'+'v'+'erred'='AVERRED'
(Other definitions for averred that I've seen before include "Asserted to be the case" , "Stated to be the case" , "Alleged, asserted" , "Claimed" , "Stated, asserted" .)