Wow...great finds! The Concept looks to be from 1978 as it was the top of the line machine. Those are some of the best carpet cleaners from Hoover ever AND well built. The DAM and Concept were totally different. The DAM was clean air and the Concept went back to direct air. They were both side suction but the Concept had a much bigger and better designed bag (Type A). The Concept used front conversion for the tools while the DAM tools plugged in the back. The DAM never had a cord winder either.
Congratulations on both Hoover cleaners. They will work hard for you and they are both well built.