Honestly doesn't matter much.
This sums it up. I think people are trying to squeeze another inch or two out of Tatum so that they it can somehow be justified that we play him out of position as a big.
Tatum is a wing. A wing with nice length, but a wing. He is not a big. The Celtics play a lot with 1 big. That seems to work fine in today's NBA but if the other team plays with 2 bigs, it creates mismatches (going both ways). This is all still true whether Tatum is 6' 8-3/8" and listed as 6'-8" or if he is 6' 8-7/8" and listed as 6'-9".
I never understood why many seem to want to take one of the best young wings in the NBA and turn him into a PF. The solution to the Celtics lack of a decent PF is not to try and make Tatum a PF. The solution is to get a decent PF on the roster (because yes, sometimes you need 2 bigs on the floor). I just don't get this.