Mormon 9:34

"But the Lord knoweth the things which we have written, and also that none other people knoweth our language; and because that none other people knoweth our language, therefore he hath prepared means for the interpretation thereof."

The Lord knows everything.  He knows what is happening now and what will happen. It is no shock that the Lord knew how to preserve these scriptures. He can perform all miracles, and He did as Joseph Smith translated the plates into the Book of Mormon.