It’s all about the end product. So if you make an intro video, that’s seen as one end product. You can use that intro video with the music as much as you want with a Music Standard License.
But if you make a new intro video and you want to use the same music again, you have to buy another license.
If you’re using the music as background music in one of your videos (one end product -> Standard Music License) and you’re planning another video with the same music as background music, you’ll have to buy another license. Cause it is another end product.
Hopes that clarifies.