Read what it says just under where the years are stated, that will give you a big hint of what's happened to Navi i.e its Navi-gated it's way closer to 2019.
To draw it out longer AMD will say H2 2018 by which they actually mean December 2018 and by December 2018 that only means they give us half baked barely working card that their charging silly money for and the RX version the one we here only care about it actually coming some time in Q1 2019.
December 2018 would be pretty good considering 7nm only starts mass manufacturing at GloFo in 2H 2018. AMD will also have Zen 2 ready which they may prioritise over Navi as well, AMD's manufacturing capacity at GloFo will be heavily contended over those two products.