They tweaked the points system when they introduced the Bonus Points. Before it was just 2 for a win, 1 for a draw, 0 for a loss. It became the same as the Premiership & Pro14 with 4 for a win, two for a draw, 0 for a loss, 1BP for 4 tries, and 1BP if you lose by less than 7. However, if a team gets a Grand Slam, they get 3 extra BPs. This is to get around the scenario where a team could win all their games without BPs & End up on 20, but the second team could win 4 games with BPs, & lose with 2BPs to the GS team and end up on 22 points.
In other words, GS beats all...