Yes, but as I say, the word case is nominative, which means that the word need not be in concord with any other word except the article. Paul is not expecting his readers to figure out what is "the perfect" from grammar construction. Rather, the context determines the meaning of "the perfect."In Greek sentences in which we find adjectives with an independent or substantive use, those adjectives still have gender, and the gender of the substantive adjective "teleion" is neuter.
Grammatically, it could refer to anything in the world. Grammar is no help in our search for what Paul meant by "the perfect." The context is a better place to search. Since the canonization of the scriptures is NOT in the context, then it is highly unlikely that this is what Paul meant. And neither does it refer to the Second Advent, which is also not mentioned in the context.Grammatically, it could be a reference to the canonization of the New Testament.