The YA-10A first flew on 10 May 1972, so the copyrights were probably registered before this date.
The copyright would have endured for a first term of 28 years from the date it was secured. During the last (28th) year of the first term, the copyright was eligible for a second renewal term of an additional 28 years. If no application was filed for renewal, the work would enter the public domain after the initial 28 year term.
Copyright and patent are subservient to the details of Fairchild’s contract with the DOD. The contract would spell out the DOD’s right to contract with other companies to build more aircraft or spare parts. You could assume that since the original jigs no longer exist, Fairchild couldn’t supply replacement wings in a timely fashion.
Maybe the Air Force holds the design patents....it was built to government spec’s