Melee Discipline Timer Groups

[Nordenwatch]

I noticed on the Wiki for all melee discipline charts it shows certain discs as being in timer groups: 1, 2, or 3.

I assumed until I got my monk to the 50's that this meant that the discs on the same timer groups would be on the same cooldown, so one could use three discs at the same time.

This obviously is not true as using any discs puts all your discs on cooldown for the CD of whichever disc you used.

Were the timer groups implemented later in the game? Or do they signify something else?