The OXCART and TAGBOARD programs were declassified in 1976 when the surviving D-21B drones were placed in outdoor storage at Davis-Monthan AFB,
Arizona. The A-12 aircraft were to join the drones but instead remained in a building at A.F. Plant 42 in Palmdale until 1981. In preparation for
placing the aircraft outdoors, the CIA in 1976 crafted a memo for Air Force officials to use in response to queries about the aircraft. In 1981, after
the A-12 airframes were moved outdoors at Palmdale, a number of historical photos of the A-12 and D-21 were released along with some general details
about the OXCART and TAGBOARD programs. "The OXCART Story," an article in the CIA's "Studies in Intelligence" magazine (published in 1976 and
1982) was declassified in 1991 when A-12 aircraft started entering museums for public display.
I wouldn't hold my breath waiting for an SR-72. According to Skunk Works insiders there has been some materials and propulsion development, but the
design still remains largely a "paper airplane."
I trust Zaph, if he says "really cool stuff", it's probably even cooler than most of us can imagine.
I would think the really, really, secretive stuff wouldn't even be handled by a military contractor. It would be easier to keep it under wraps if it
was done "in house". That's just a guess though.