Apparently there is a Navi 12 gpu in the works.
Navi 10 - 5700, 5600 series
Navi 14 - 5500 series
Navi 12 - ??
Czech website diit.cz speculates that Navi 12 could be custom gpu for Apple / Microsoft mobile devices.
It is rumoured to have much lower base clocks and HBM memory too.