Let's be realistic. If they are really going to deliver in September. Then, they should be tweaking some prototype NOW, OR at least show us some photo of their 28nm chips, OR at the very least, some photo of the shinny wafer. But do we see any of those?
What are you talking about? You design a chip. Then you send it off to the fab to fabricate, dice, and package. Then you wait three months, and then you get your chips in the mail.
The only way to get "prototype chips" is to do a small order early, test, and then do another order later on. But that process takes 6 months.
If you do your whole order up front, then there
are no prototype chips, they are never created in the first place. KnC will get it's first chips in September, and those will be sent out to customers.
There is a small chance the chips won't work, but that's unlikely.
If you think they'd have prototype chips at this point you don't understand how ASIC production cycles work.
He's probably thinking about full miner prototypes containing the ASICs.
Actually the first batch of chips are often called prototypes. The vendor will package a smaller amount of chips of your first run. You will receive the packaged chips and you then have to do a prototype approval, which usually means to mount the chips on a PCB and start running SW etc. If everything is OK you will accept and the vendor will continue to package the remainder of your initial order. If you discover a problem you can stop the process and not package the current batch of dies and halt production. Usually you will have to pay a fine (given in the contract) since the vendor/fab has allocated resources for you, but this will typically cost you less than a full inventory of packaged useless chips.
Then you have to test the product containing the ASICs, especially pay attention to power and EMC issues. It's not uncommon that you will discover some problems which requires a new PCB update, better shielding of the enclosure, a metal fix for the ASIC, or even a full re-spin (fortunately a miner is a pretty simple design, there is no high speed serial interfaces like PCIe, or DDR3 memory interfaces, typically only a couple clock domains, etc so this might not be likely). Then you will have to take the compete unit to a certified lab to get approvals required by the country where you plan to export the devices. This process takes several weeks and I would have expected KnC to have their ASICs in house by now (or even for several weeks) in order to be able to ship next month.