the SDK's seem to follow the PS3 firmware revisions so during the development of the launch titles there were probably a few different version up to v1.0 (that's if the PS3 actually shipped with 1.0 firmware at launch, I can't remember). But none of those SDK's were leaked, I think the first one that made it public was 1.92 but I might be wrong on that.
Actually the earliest Sony SDK to surface was 1.60, then 1.92 & 3.41 respectively. In regards to your question, most likely it was the IBM Cell SDK 1.1 that was first used to produce content for the PS3, early development was a joint project by Sony, IBM, and Toshiba I believe.
These SDK's along with TONS of other documentation and published resources are all disappearing from the net at an alarming rate. I am going through my massive libraries today and just happen to see your post on a break. If you need something you are all more than welcome to ask, if ANYONE needs something and I have it they can get it with a swiftness.