Mormonism & The Sufficiency Of Scripture

I recently read an LDS member’s statement about the alleged insufficiency of Scripture.  According to him, the Bible doesn’t contain everything necessary for our salvation. Here is my reply: 

So what you’re saying is that the Scriptures of the Old Testament didn’t contain all that is necessary for salvation.   How did the Hebrew nation muddle through?  How was anyone saved? 

The implication of your words is that the Old & New Testaments both individually & collectively did not testify all that is necessary to be saved, which implies either nobody whatsoever was saved or that some people were saved in spite of the lack of sufficient information/instruction. 

How does that work? If you say nobody was saved, that contradicts LDS theology that people were saved in the OT era & that the gospel was preached in every age.    

If people were saved & the gospel preached in those days, then the OT does contain all that is necessary to be saved which contradicts your statement about the insufficiency of the Bible. 

LDS faith & practice turns on the idea that the gospel was lost after Christ, ergo the need for a restoration of the faith.  If true, then sufficiency really isn’t  a property of Scripture as much as it a property of the mind.  

Here’s how: 

If the gospel was lost, then it was lost after a period in which it was operative, which means that at one time the Scriptures from which the OT Prophets & NT Apostles lawsuited & taught did contain the necessary information for salvation, ergo there was a time in which they were sufficient w/o LDS literature.   

Then the understanding of the people became so muddled that a restoration was required, so the problem isn’t the clarity & sufficiency of the Bible, the problem is the understanding of the people — which a property of the mind, not the Book.