Book of Mormons or Books of Mormon?

At church today, our teacher in Sunday School was sure to tell us (in the middle of lecturing about missionary work), that when talking about more than one copy of The Book of Mormon, that it's "Book of Mormons," not "Books of Mormon" because that is the right grammar stuff. As is always the case when someone presents something as fact, I thought on it for awhile to see if I agreed. After some wordplay, I decided that if we're going to be grammatically correct, then it is neither "Book of Mormons" nor "Books of Mormon," but "copies of The Book of Mormon."

How did I arrive at this conclusion? It's quite simple, really. Think about another title of a book. Perhaps Inkheart or The Book of Virtues. Any title will do. Now try pluralizing it in the first instance, and see how it sounds. So instead of "We gave out Book of Mormons," we'll try this: "We gave out Inkhearts." It sounds a little strange. It can work, but it doesn't seem exactly right. So then we try the second instance. "We gave out Books of Virtues." Again, it can work, but it is still only second-rate, at best.

This leads us to my own contribution. "We gave out copies of Inkheart" and "We gave out copies of The Book of Virtues." In the end, it is the only thing that truly makes sense. In the other cases, the meaning is understood, but it isn't really correct. A similar case would be if I were to say "That car don't work" or "I be a girl." You would understand what I was trying to say, but it wouldn't be the correct way to say it.