Joe Bemier wrote:
Not correct - Coping will immunize against deviations far more than
cutting compound angles.

While it's true that a coped joint will hide deviations better than a
mitered one, either will reveal errors as small as 1-2 degrees - which
is why I wanted to point out to the OP that he should check the corner
angles before coping. I did not advocate using miters for the final
installation - only using mitered test pieces to measure the corner
angle. It is precisely because of the miter's sensitivity to corner
angle, and its relative ease of cutting, that I recommended making the
test pieces in the first place.