Marko Mattila, employee of Jolla had a showcase on Sailfish SDK at FOSDEM and it came up that the SDK would be available by end of February. Jolla as a company never confirmed that, so I think we have to be careful with that.
I've never heard them say during/end summer, but could have easily missed that. Maybe they meant availability by end of summer?
Personally I always compare the Jolla device schedule with the N9 schedule 2 years ago: February: Rumours, but non presentation of device (N9 and Jolla device) June: Presentation of actual device (N9 so far) September: Public release of phone (N9 so far)