The scriptures we have are a covenant with us and God. The more we honor the scriptures we have received, the more likely the Lord is to reveal additional scriptures to us.
The Ancient American prophet Moroni spends almost an entire chapter on this in the Book of Mormon, when he discusses the sealed portion of the Book of Mormon which includes grand visions of all the things to come including that which was shown the Brother of Jared (Moriancumer) (Ether 3:21-28), that will only be made available when the saints have the faith like unto the Brother of Jared (Ether 4:6-7). The same promises apply to the visions of John the Revelator (John the Beloved) (D&C 93:6).
Additionally, some acnient scripture scholars note that Enoch himself wrote 366 books, as the "Scribe of Righteousness" and kept them as the Book of Enoch - which has been hidden from the world because of unbelief. Yet, this additional scripture, namely, the Book of Enoch would help fill the world with the word of God in the last days, as prophesied by Joseph Smith, and eventually be revealed (D&C 107:57).
The promises and prophecies of Enoch and Moriancumer are not the only jewels of wisdom and light we are promised to receive as we obey the new and everlasting covenant, namely the Book of Mormon (D&C 84:57). In fact, as we clean and sanctify ourselves with God's word (John 15:3) we are promised to know all things, including the prophecies and promises of all God's prophets; and there have been many prophets.
Zenock, Jasher, Abel, Seth, and many, many, many more, are just the tip of the ice berg. And why wouldn't it be that way? The Lord tells us "whatsoever [Elders] shall speak when moved upon by the aHoly Ghost shall be scripture, shall be the will of the Lord, shall be the mind of the Lord, shall be the word of the Lord, shall be the voice of the Lord, and the bpower of God unto salvation." (D&C 68:4). And in Amos 3:7, God promises us He does not do anything unless He reveals His secrets to His prophets, suggesting there are many books of scripture that have been hidden from the world; waiting to be received by the faithful.
We also know that Joseph Smith was shown the records room or "Cave" where Moroni and many other prophets kept the unnumbered records of all the doings and prophecies of the Nephites. It was from here that Mormon and Moroni pulled the most precious scriptures for their descendents and preserved and abbridged them in the Book of Mormon, so God could "restore his people". An exceptional scholarly summary written by Cameron J. Packer, published in 2004 at BYU, records various references to the cave of records and is available here.
Specifically, he notes "Brigham Young said that when Oliver Cowdery and Joseph Smith were in the cave [a] third time, they could see its contents more distinctly than before. . . . It was about fifteen feet high and round its sides were ranged boxes of treasure. In the centre was a large stone table empty before, but now piled with similar gold plates, some of which lay scattered on the floor beneath. Formerly the sword of Laban hung on the walls sheathed, but it was now unsheathed and lying across the plates on the table; and One that was with them said it was never to be sheathed until the reign of Righteousness upon the earth." Id.
To point us all to Christ, the source of all God's word here below, I have compiled over 130 references or inferences of additional scripture yet to be revealed, I have found in the scriptures, over the last few years. I hope they help you price the Word of God, and treasure the power of His constant call to us through his ancient and modern prophets. May we all be cleansed by His word (John 15:3) and look up the Zion, as they look down to us and join us in building heaven on earth.