Mormon finished quoting the sermon that Alma delivered to the people in Gideon. He moves to the next sermon he wants to include, but he needs to set up the story and, therefore, he returns to narration. In this section of the Book of Mormon, the current chapters follow the boundaries of the original chapters. That is helpful because it helps us understand how Mormon is using his source. Chapter 6 was Mormon’s narrative interlude that finished the story of preaching in Zarahemla and going to Gideon to preach. Chapter 7 was the quoted sermon. Now, in Chapter 8 we have the narrative history that will set up the sermon that begins in Chapter 9.
One of the features of the times, that Mormon uses the large plates as a source, is the marking of the years. In this case, however, it is possible that the marking of the years was also on Alma’s personal record. Alma was the one who introduced that system and mentality to the large plates, and it wouldn’t be surprising to find that he also used it in his personal record.