Maybe that is how this particular person/music company does it. I don't think the way music is written is entirely standardized.

Notations, symbols, etc have evolved over the centuries and between people in the same century. I think areas people live change the way some music notation is written, also. I remember in cello, violin and viola lessons, the instructor obtained old early sheet music by, I think it was Bach, and it had some strange notations. He had to explain what they meant. Then he found a better translated one that was written the wy it is done today. I think it was Schumann(?), not Bach, but the idea is the same.