I found out that many tracks are not shown as results when searching.
If you search a song writing title & artist in the bar, you have a number of results much less than what actually Deezer has.
You can notice by a simple operation: only search the artist and open some of the albums related to him/her; you will soon find an album containing the song (above mentioned) not shown in the former search.
This means that sometimes, when you can’t find a track, it is only a malfunction, it is actually owned by deezer but not shown.
Am I wrong?
Thanks for your help