This brings us to some details that need to be understood. The clarifications in verses 41-44 were a result of the "mechanics" of how the practice was implemented. The various efforts to "fulfill the law" while still keeping up Elizabethan appearances included performing a "sealing" for time and eternity to one man, while the woman was married for time to another man. This relieved the eternal husband/companion of any duty to have conjugal relations with, or provide financial support for the woman while here. It allowed her to live a "normal" married life with her husband, while still committed eternally to another. A sort of nod in the direction of the plural wife revelation, without any real commitment to actually practice it here. There were other forms of compromise attempted, as well.
The defining of what was and what was not "adultery" was necessary in light of the troubles on the ground, so to speak. Confusion began to multiply as these compromise efforts were attempted by people who really didn't want to get this thing going in the way David and Solomon had done.
Also, verse 51 grew out of a specific incident in which Joseph and Emma were arguing. She protested his secret addition of more wives (beyond those she had approved) and was complaining to him about it. In response to the arguments, Joseph offered to have her marry William Marks (the Nauvoo Stake President) as well. This is what is referred to by the oblique reference: "that she stay herself and partake not of that which I commanded you to offer unto her." This, again, was an event in the 1843 time frame. It could not possibly have been part of what was happening in either 1829 or 1831 when the first part of the revelation was received. Showing once again this was an amalgamation of several revelations, and not a single transcript.
Not everyone in Nauvoo knew what was going on. Nor was everyone who practiced this principle discrete enough to escape notice. Enter John C. Bennett, who had abandoned his wife and children and come to Nauvoo pretending to be something more than he was. He got added to the First Presidency and elected mayor of Nauvoo. He learned of the commandment, and then began to let his libido go in Nauvoo. He produced a system of seducing other men's wives under the practice of "spiritual wifery" which he would later blame upon Joseph Smith. Indeed, John Bennett's account of Joseph's exploits seem more autobiographical of Mr. Bennett, with Joseph given credit for Bennett's wrongdoings.
As I said before, this was not a culture into which this commandment fit neatly. It was awkward. They just didn't know how to do it, nor what would work or not work. Even so basic a matter as the definition of "adultery" became hard to sort out. The half-way measures Joseph tried to implement in order to avoid the outright practice were not working. They were producing such confusion that these verses were needed to sort the mess out.
Trying the souls of those who were involved, indeed! Proving whether you have faith to sacrifice everything for God, indeed! This was terrible, difficult stuff. Not the license for a libido that critics were trying and still try to make it seem. Even Bushman has mentioned how few offspring Joseph Smith produced as a result of the plural wife system. It seems that the only offspring Joseph ever fathered were through Emma. (Of course we have the tale of Eliza Snow's miscarriage, but that child did not live. So far as has been documented, all Joseph's living descendants came through Emma, despite DNA testing of other living descendants from putative children.)
Look, we should have compassion and empathy for these people. They didn't want it any more than a normal, mature and moral person living today would want this. They were draftees, not volunteers. It was quite hard for them and even harder on them.
Anyway, I still am not to the answer to the question, just laying the groundwork to understand the answer first. I'll write some more on this as I have time.