Confirmed the existence of AMD Polaris 20
Our colleagues found in driver 3D-card series Radeon RX 500 mentions of AMD graphics Polaris 20. More specifically, the model-based Radeon RX AMD called GPU 580 Polaris XTX is 20 and the model-based Radeon RX 570 — AMD 20 Polaris XL.
For series Radeon RX 550 used entry-level under the name Lexa Pro. Series Radeon RX 560 is not in the list.