I'll add that if your equipment is accurate, you were at worst 66.9+1.5 brix which is 68.4 brix which is still in spec. (68.9 is the max in all states and I think Canada too)
The murphy cup tells you the reading that is equivalent to 66.9 brix.
Which by the way is the legal minimum in Vermont and New Hampshire.
I realize you are in neither of those places, but the point is that its better to be over the murphy cup reading than under.
I am in Vermont, and although I don't really sell (only sort of), I consider the murphy cup reading the bare minimum and go at least one point over.
So, I'd say, you're spot on!