Heath Kirchart 360 flipped the small one in Birdhouse Ravers (1992). If I'm not mistaken, that move alone got him on Hawk's company. Pretty impressive for its time.
As someone said on here, the big one is not just an 11 stair gap. It's really intimidating. There is a wall at the bottom, the landing is uphill, and the takeoff is not ideal. I wasn't with him, but I heard that Jim Bates went there sometime in the early/mid '90s. Being the fucking stair king (he had already kickflipped a few 12 stairs), you'd expect something big. He skated the little one all day, then finally mustered up the courage to tackle the big one -- with just an ollie. (Say what you will about Jim, he was one of the best stair skaters of the mid '90s...I filmed him trying to backside flip the Santa Monica Triple Set...came close but no cigar...he would have been the first one to do that trick down'em.)
Wasn't there another gap there? Jeron heelflips it in his amazing 411 Wheels of Fortune (issue #3) and Koston switch backside kicks it in Goldfish. I think that one is there too.