A gull wing configuration for tailless aircraft stability & control was patented by Grumman-Bethpage in 1996, filed in 1993*.
Grumman had been shopping around an unclassified flight demonstrator concept using an X-29A to NASA, AF and DARPA, to no avail.
[*Rich Nastasi conceived of the idea in 1987 or 1988 in a classified environment; I know firsthand.]
-------
Grumman didn't file for the patent until a year after McDonnell Douglas-St Louis 'reportedly' began work on Bird of Prey.
Guess#1 is that Rich's concept was wind tunnel tested in 1988 or 1989, and the results made their way into the sanitized technology-leveling library administered by the LO/CLO EXCOM. McAir, AF and/or NASA became aware, and adopted it.
Guess#2 is that McAir cooked up the gull-wing control effector configuration themselves -- nothing new under the sun, as they say.
I lean to Guess#1, owing to some technology transfer shenanigans I'm aware of with the nozzle design on Bird of Prey and the near-concurrent X-36.
