I agree with you, as I stated. Your use of the laws of logic are sound. But to expand on what you said, there is only one truth. Truth is exclusive. If we say something is true, then all other possibilities are false.
Look, in marriage, to be "true" to one and only is indeed exclusive.
And, truth disseminated is "locked in"...but truth on the receiving side is not often as "boundary-ized" as we present it.
We want to carefully codify it. And too oft limit to who's receiving it -- and of greater import, receiving Him who is truth: Jesus said: "I am the way, the truth, and the life. No one comes to the Father but by Me." (John 14:6)
Iow, Jesus Himself is the Personal Living Truth; and His relationships extend beyond who we want to carefully hermetically seal them around.
Jesus is the Living Truth, the Living Way -- the exclusive Way to the Father. Yet He also said: 39 You study the Scriptures diligently because you think that in them you have eternal life. These are the very Scriptures that testify about me, 40 yet you refuse to come to me to have life. (John 5)
Iow, some people relate only to the Bible -- failing to realize the Bible simply points to Christ as a current living relationship lived out 24/7 (see John 17:3).
They wind up aborting this process about "truth" -- relating to pieces of paper -- vs. the Living Truth, Jesus Christ.
Truth as propositions are indeed "Fixed." And Christ Himself doesn't change. Just don't pretend that your "beat" on Christ as The Living Truth is so precisely "fixed" that we are able to "rule out" who some of His people are -- or will be.