https://www.kncminer.com/news?page=3
There is a list of known preorders here:
https://bitcointalksearch.org/topic/kncminer-list-of-orders-october-delivery-249065
If I count the number of the number of rigs preorders on that list up to june 11th, I get 95 jupiters and 47 Saturns. That means ~16% of all preorders were on that list
The total number of preorders for batch one on that list is 146 Jupiters and 68 Saturns. If the same % of customers posted in that thread as for earlier orders, that would mean KnC actually got 6.2x more, or
589 Jupiters and 291 Saturns.
589x400GH + 291x200 = 293TH
Substantial, but no were near enough to quadruple difficulty.
Each of those 890 orders may have more than one device in their order, therefore your extrapolation represents a bare minimum estimation. I do, however, share your sentiment that quadruple difficulty is absurd.