A friend at the Robinson Safety Course just got confirmation from Tim Tucker (Chief Instructor at Robinson) that YES we can pull the additional 1.5 in. Hg (if it is there - see the bit in the SN-25 about high DA).
If this is the intent of SN-25, then another amendment of the POH is required. As it stands, manifold pressure limitations are published in section 2, and placarded in the cockpit. As long as this doesn't get amended, you can still not legally use more MAP than what the limitation chart tells you, carb heat or not.