There will be another pre-release discount offered on 9 Sept, if my memory serves me right. I recall reading that in a Sengoku facebook page entry, but I doubt it will be 20% off.
I guess we need to keep an open eye/ear for the official word on the 2nd discount offering.
edit: here is the post:
"Sengoku We're sorry that some of you missed the Facebook pre-order.
Shane, we did send out a message to everyone as well and when we discovered that many didn't get that, we posted it under the like us tab and under discussions. There will be a pre-order offer with another bonus of some kind September 9th. Hold on until then!"
See? My memory STILL works!