No, you didn't miss it. The sale goes through the month of August. The email flyer says this :
25% Off
All NOS Tubes through August 31, 2013!
No brand selecting.
Select a NOS tube and notice the price has been slashed with a line through it. That is the sale. It appears that you cannot select the brand of tube, only the tube type by number, and NOS. I think you get what you get and that is that.