NW did operate MD80s they acquired with the RC
merger, and the MD80s lasted into the late '90s, BOI
was served with MD80s at least to 1998, before they switched the route to 727s. The MD80s were victims of fleet simplification just like the 727s NW
used to operate. The MD80s also flew out of both MSP
after the merger. Also, the MD82 and DC-9-82 are the exact same aircraft with different designations. The MD82 designation was adapted to get away from the DC designation that had a somewhat degrading PR
value in the early '80s, especially after AA191.