Along with the seasonal nature of warfare, it is also possible that not all of the opposing armies were always the ones to fight the battles. At this point, they are simply the enemy, and Mormon makes no real distinction as to which groups might be attacking them.
It was also true that the early flight of the Nephites before the Gadianton and Lamanite armies at the beginning of this chapter did not mean that the Nephites were never victorious. In that case, they were. The problem was that it was not a lasting peace, but only a reprieve. The inexorable march toward Nephite destruction was on.