Accuracy glitch
From Ephinea PSO Wiki
The accuracy glitch (also known as the SN glitch or SNS glitch) is a bug that allows the player to overwrite the accuracy of a ranged attack with the accuracy of a later attack in a combo.
The combo step (1, 2, 3) updates when the later attack is input but the attack type (N, H, S) is updated when the animation for the next attack starts.
For most projectile weapons this means that S1 can be glitched to have N2 accuracy (for example), but melee weapons that can be glitched S1 could only take on S2 accuracy.