2017, I mean technically 2016, they're just the RX 470 and 480 with a new die revision so they can hit higher clocks. You can flash many RX 470's and 480's to RX 570's and 580's as its mainly a clock speed and slight power increase, and most of those could tolerate the increased clock and power settings.
Some OEMS actually didnt change a thing on power and clocks and just changed the name. So a Dell OEM RX 480 and RX 580 are exactly the same card, just with a different name. This was a thing because AMD never release a reference RX 580, they just told the other OEM's to have fun. So some RX 580's have exactly the same clocks as the RX 480 (1266 boost), and others shoot up to 1430 boost. We also have the RX 590, the RX 480's 12nm final form, up to 1580 boost clocks.
I think Polaris is AMD's best GPU architecture, it was never the fastest, but it was good enough, and it was there when the company desperately needed it. Its interesting to see it still around, and somewhat relevant for low end gaming, almost a decade after its release.
RX 480
https://www.techpowerup.com/vgabios/184327/amd-rx480-8192-160603
Dell RX 580
https://www.techpowerup.com/vgabios/194686/dell-rx580-8192-170301