bags - hopefully 3FingeredGlove will see your post and comment. I don't know what the rules are but I think I might know is going on here.
I think the NLI is only a valid contract for the first year of attendance. Thus, if tuition would have been raised during your son's first year of college, then they would have been obligated to raise his money based on the terms of the NLI - in this case the percntage of tuition. After the first year however, they can raise or lower the scholarship amount as they see fit. Thus, I believe they are under no obligation to raise his scholarship amount at this time.
Now, for political purposes, it might make sense for them to increase your son's dollars i.e., they don't wnat the word getting around that they are not honorable with their players.
Hopefully others will correct me if I am wrong about this.