Tech actually has 4 National Championships. 1990 being the only modern one, but Georgia's last was in 1980. Clemson's in 1981 as you've stated.
The NCAA doesn't recognize football national champions prior to the 1950 season when the "consensus" clause came into effect. They were essentially "self-proclaimed" prior to 1950. So, based on NCAA criteria, Georgia Tech and Georgia each have one. With that said, if my school claimed one, I would certainly count it as well.
https://en.wikipedia.org/wiki/College_football_national_championships_in_NCAA_Division_I_FBS