I have noticed that most often a relative pronoun such as who, which, etc. is used to further inform the reader about its preceding noun or noun phrase, e.g.
1-Do you know the girl who is talking to Tom?
2. I told you about the woman who lives next door.
3. The man who did this is the brother of our neighbour, Mr. Smith. 
In both statements above, the precedes the noun, i.e. girl and woman, respectively. But, my question is:
Are relative clauses always a justification for using the definite article "the" before their antecedent?
For instance, in the following statement, individuals is not specifically known of in the context, and thus the only introduction for that comes in its relative clause who had not taken part.... Has the been used correctly here? Or should it be omitted?
... and providing questionnaires to the individuals who had not taken part in the coordination meeting of Khuzestan soccer referees
-1 and 2, http://www.ego4u.com/en/cram-up/grammar/relative-clauses
-3, Tipping, L., Matriculation English Grammar, 1967