This is more than interesting. The Lord speaks, various people write what He speaks to them. These groups include:
1. Jews-- we get that and it's the Bible, right?
2. Nephites-- we get that too, the Book of Mormon, right?
So, let's take this a bit by bit, going through each one:
1. Jews: We have a Bible. But we DON'T have all the writings of the Jews, do we? We already referred to missing prophets Zenos and Zenok, and there are others. Look in your Bible Dictionary for "Missing Scripture" and you'll tree a list. (I'm pulling your leg. If you look that up it'll refer you to "Lost Books" so go there.)
[That reminds me of a joke I tell: If I get a tattoo it'll say "Leviticus 19: 28." But you probably won't think that's funny.]
Anyway, the Jews recorded more both in the Old Testament and in the New Testament than we have currently. So don't get all certain the Bible is the final word from the ancient Jews. It isn't. Never was. There's more coming.
2. Nephites: Clearly more coming. Sealed material has not been revealed, and will be some day. Providing, of course, we were to actually merit the disclosure. So, I suppose that means don't hold your breath.
3. Other Tribes: We got nothing. Not even a number. The one chance we had to get a number was blown by both the disciples in Jerusalem and the Nephites. I've written about this in The Second Comforter. So the only way to triangulate is to either take the allegory of the Olive Tree in Jacob 5 and try to estimate-- a risky proposition since it was intended to convey an overall meaning not a number-- or we can work backwards from the crucifixion to the approximate 11 1/2 months later when Jesus appeared to the Nephites. Take the time spent with the Nephites, then estimate He's been busy doing that same ministry elsewhere. Divide the time taken to minister into the available time and you get something between 10 and 18 other potential groups out there depending on your estimate of the time used. The record attempts to prevent us from being too accurate because it identifies three days specifically, then resorts to just "many times" to cover what may have been days or weeks. (3 Nephi 26: 13.) However, when you read of the Nephite disciples "journeying and preaching" but coming together in "mighty prayer and fasting" and the Lord's appearance again there, it seems closer to the 10 number than the 18. (3 Nephi 27: 1.) Well, you work it out. It's just an unknown plural number which might be greater than just a couple. And for these we have no record at all.
4. All nations: Nothing here, either. And no basis from which to compile an estimate.
So, from the foregoing we can see that we have some tiny fragment of the whole, and cannot even begin to construct an outline of what we are missing. But despite our ignorance, the Lord spoke to them, they wrote it, and it is available for some group to eventually read. Apparently not us. We do not even get the rest of the record written on parchment and hidden by John, (referred to in the headnote to Section 7 of the D&C). We only get a part of the information from it. (D&C 7: 1-8.)
So, there's a lot to be had. We don't have it...But what we do have we won't study. Well, maybe there is a cause and effect...
Seems to me, you don't want to talk about it. Seems to me, you just turn your pretty head and walk away. (Joe Walsh, from the James Gang era, before the heaviest toll was taken.)
So the Lord wants us to know there's ever so much out there. That we have a tiny fraction of what was once available. And we just don't seem to care. We'd rather reduce the volume of topics we study and eliminate the "mysteries" from our diet of Gospel study, so as to relieve ourselves of any responsibility for what we already possess. We are beyond dumbing down the Gospel. We're discarding it by the week. Tighter and tighter, until you are left alone, without God in the world. There's a brilliant phrase. It comes from the Book of Mormon. It is found at Mosiah 27: 31; Alma 41: 11 and Mormon 5: 16. Of all the phrases turned in the Book of Mormon this is the most solitary, profound and descriptive of the fall from grace mankind experiences. It is perfect, even if what it describes is perfectly horrid.
Well, enough of this...