Disclaimer things first: take this with a grain of salt, since this hasn't seen the amount of confirmations we'd like. 3D Center has come out with a table that supposedly demonstrates the schedule of RX Vega manufacturing and integration work from AMD's add-in-board partners (which includes the likes of Sapphire, XFX, PowerColor, and others.) Remember that manufacturers receive a suggested reference design from AMD as to how to incorporate their GPUs into an actually operable graphics card, with varying degrees of customization according to the particular partner we're talking about. And this process takes time.

According to the leaked schedule, the BOM (Bill Of Materials) for the required parts to properly manufacture an RX Vega graphics card was to be released sometime in June, with engineering validation tests going through the end of June towards the beginning of this month (July.) Actual working samples from AIB partners are scheduled to be available in the middle of this month, with product validation tests (PVT) stretching towards the beginning of August (you'll remember AMD has confirmed they'll be formally announcing the RX Vega graphics card(s) at SIGGRAPH 2017, which stretches through July 30th and August 3rd.)