I'll never understand why people do this. "_______ was ROBBED!!!!!" And the same person has it 115-113. Like it's entirely impossible for someone to find one round different from the poster. There are cases when you have very clear and close decisions, but 95% of the time, a 115-113 will carry a bit of controversy either way.
You can score a fight 115-113 and still claim robbery if the guy you scored the fight for clearly won 7 rounds. However, that didn't happen in the Dawson/Johnson fight. There was probably about only 3 or 4 rounds that Johnson clearly won.
But it would have to be beyond the shadow of a doubt. How many times are 7 rounds entirely clear? It has happened -- Morales/Pac I, for example -- but it's rare. And as you say, Dawson/Johnson was difficult to score in the latter half of the fight. I rewatched it last weekend and got Dawson winning 7 rounds. I could find 7 for Johnson too, though.