I thought that when you add an artist, you add all the existing music with them. However, some of the Patricia Kaas' (a quite well-known French singer) albums that include some of the most popular songs are somehow missing... Quite surprised to only see around a half of her music.
Thanks for searching for the answer you need here!
Spotify works hard to constantly add music to its content database. However, keep in mind that content availability can vary over time and between countries, depending on agreements between Spotify and rights holders, such as artists or record labels. This might be the reason you can't see some of Patricia Kaas' albums on Spotify.
We add new content to Spotify every day, so if you can’t find something you’re looking for right now, it may appear (or reappear) soon. Alternatively, you can always contact the artist or record label with your query as well.
Hope this helps. Let us know if you have any more questions.