If that were a false statement, then it would violate the law of non-contradiction. By all means, please explain how it is in accordance with reason for that statement to be both true and false.
Ok
Here is your original statement...
Either
Acts 15:19-21 contains an exhaustive list of everything that would ever be required of a mature Gentile believer or it does not
The reason your statement can be false, without violating the law of non-contradiction is because you include the word "ever".
The law of noncontradiction is great, I love it
What the law of noncontradiction says is that contradictory propositions cannot both be true in the same sense, at the same time.
Notice "at the same time".
When you put the word "ever" in your sentence it makes your sentence mean "this list must be exhaustive or not exhaustive, both when it was issued and forever after."
What I am saying is that the list was exhaustive when it was issued, but later on it was changed. I'm not saying the list was both exhaustive and not exhaustive at the same time (that time being when it was issued).
Using an illustration, If I were to say "Jim is alive right now, but he is also dead" this could be correct, if I was using "alive" and "dead" in different senses. So he is alive physically, and he is dead emotionally. But it would be meaningless contradiction if I meant it in the same sense, both alive and dead meaning literally physically.
Similarly if I said "Jim is alive" and two weeks later I said "Jim is dead" that would not be a contradiction if Jim had died in the meantime, because I'm not saying it at the same time.
Another point that is worth making here, which a lot of Christians seem to no longer understand, is the difference between doctrine and discipline.
The authority of binding and loosing dealt with the application of the law. Those terms were used among the Jewish rabbis to describe their authority to allow a practice or a forbid a practice as an application of the law to daily life.
That is discipline.
Doctrine is about teaching spiritual and moral truth. That would be equivalent in the OT to saying what the Law IS and how it should be understood.
Discipline is about application of truth to moral practice based on current circumstances.
Doctrine is about elucidating moral and spiritual truth.
Disciplines can be changed and they are usually not moral absolutes in themselves.
Doctrines, can develop as we grow in understanding, but they cannot change in the sense that it was once true and now it is not true any longer.
For example, forbidding eating meat offered to idols was a discipline. It was forbidden because it was seen as a dangerous practice culturally and avoiding it was good for both individual spiritual health and the spiritual health of the community. Paul makes this clear when he talks about eating meat sacrificed to idols. He clearly teaches that it is not inherently immoral. The council forbade it because of practical reasons, not moral reasons. The same is true with eating blood and eating things strangled.
Sexual immorality, on the other hand, is not a matter of mere discipline. It is a matter of doctrine.
The Church has the authority to remove or add disciplines as circumstances change. Once sacrificing animals to idols was basically eradicated from Western Civilization, the prohibition against eating things sacrificed to idols was no longer necessary because it could not cause scandal to the Church and hurt the faith of our brothers. As a result, it was removed.
The Church cannot remove doctrines. As such the Church cannot and never has said it is now ok to engage in sexual immorality.