The offset swashplate is rotated so that the blade's pitch angle increases with aft laging motion. This is called "alpha 1 coupling", and it makes the blade a bit more stable, and it also makes a bit more collective pitch available. The way it works is that the swashplate horn is behind the blade pitch horn, so the pitch link must lean forward to meet the blade. If the blade lags aft, the pitch link stands more vertically, and is therefore a bit longer, and makes more angle on the blade. This helps damp any lag motions.
The change was made as the gross weight was increased from the A to the B.