Ah, now I see the problem. You are laboring under the belief that something is authorized only if it recorded in in a book. (Are you perhaps one of the "sola scriptura" folks?)
In contrast, we believe that something is authorized if God tells us so; the revelation may or may not be written down later.
In some relatively rare cases, a written revelation may be presented to the Church for inclusion in the standard works; if accepted, such a revelation becomes binding on the entire Church. The process can take some time. For instance, the revelation of the redemption of the dead received by President Joseph F. Smith in 1918 was finally included in the Doctrine and Covenants (as Section 138) in 1976.
Our canon of scripture is not closed because the heavens are not closed. Consider the Ninth Article of Faith:
9 We believe all that God has revealed, all that He does now reveal, and we believe that He will yet reveal many great and important things pertaining to the Kingdom of God.
I expect many great and important things to be revealed that are not already written in the standard works.
You have NO way to prove that what you are doing now is what GOD told someone in the past to do, if it's NOT 'written down' somewhere.
Quite the contrary, we have the best proof of all: we can ask God himself. Through the Holy Spirit, we can know the truth of all things.
I expect many great and important things to be revealed that are not already written in the standard works.
So it's entirely possible, that some lad of today, searching for truth in the world, will be led by some Personage(s) to find some titanium plates in a sand dune in New Mexico and to be told that all the LDS wards are in apostacy and he will be the One to lead the confused into a Total & Complete Gospel.