During the First Vision Council Joseph received guidance, counsel and instruction as to how the kingdom of God would emerge in this dispensation with his role as testator coming more into focus.
As such, it is almost certain that Joseph was invited by Christ to see and feel the wounds of crucifixion, the nail prints in his hands and feet and thereby was able to fulfill his role as Testator on earth.
Christ showing the wounds of crucifixion to the apostles. (click for larger)
We may rightly surmise that Joseph had such a physical witness since we know that the resurrected Christ made a specific point to show the prints of the nails in his hands to the apostles at Jerusalem as well as to Thomas on a separate occasion and to those in the western hemisphere where the entire multitude went forth:
"..and thrust their hands into his side, and did feel the prints of the nails in his hands and in his feet.."
This behavior seems to be a significant part of the personality of Christ and a common manifestation of his divinity to those he comes in personal contact with as occasion permits.
However, the highly personal nature and the sacredness of such an event would certainly preclude its telling to the general populace.
As the pre-earth Testator it was proper, right and necessary that Joseph be part of the Divine Council.