I am still bemused that this was unfamiliar to a good member of the church I ran into, so I am simply posting it as a quick note.
The gospel in its fulness existed in the beginning. Adam and Eve had the fulness of the gospel. In fact, Adam was alive when Enoch was alive. Certainly Enoch was part of the meeting at Adam-ondi-Ahman. And Enoch built a Zion that was taken up into heaven. That requires all the blessings of the gospel. It even requires blessings that haven't yet been restored to us.
The law of Moses was a lesser law, given when God's people were too hard hearted for the full gospel, but good enough that he could still call them his people.
But before the law of Moses, the full gospel existed and was taught. In fact, we have not yet had a full restoration of the things that have been lost that were had by the ancients before the law of Moses. One day, we will.
The fulness of times will have all the blessings of ages past. This is not because god made an arbitrary decree about the matter. It is because Zion can only be built on a foundation that includes all the blessings of the gospel.
Obviously, those blessings already existed in the past. They were had by Enoch and his people. And by Melchizedek and his people.
And we need them restored in preparation to build Zion once again. Thus all things will be restored.
But they were had before. The new gospel IS the ancient gospel, had by Adam, Enoch, and Melchizedek. That is why the restoration involves old testament and new testament prophets appearing and bestowing keys they held once again to the earth.