I combined an Enchanted Book that had Power IV and Efficiency IV with an axe that had Unbreaking III and Efficiency IV. I expected to receive an axe with Unbreaking III and Efficiency V. What I received instead was an axe with Unbreaking III, Efficiency V, and Power IV. If my memory serves correctly, in 1.10 (and presumably previous versions), you could add enchantments to non-corresponding tools, it just wouldn't show up on the tool post-enchantment.