My question is why even delay shipment of D3 till September why not just start shipping now? I highly doubt that products are not completely built so what really is holding back the shipping of them?
They probably started sales after their first pre-production run to make sure their chip design was good and so that they could advertise accurate values. Once confirmed, they setup the sale to customers for batch 1/2 and sent the final order to the production foundry. A 2-month turn-around from the foundry is actually pretty impressive considering how small Bitmain is compared to the others who are ramping up their production at the same foundries (Apple, for example).
their internal mining schedule for built units is in the 1-6 month range, depending on the market. If you think you're getting money-printing machines right off the production line, you're naive.