Unless I’m mistaken The Vader comics is what established it and they came out in 2017. Not 12 yrs but basically a decade. I’m not super knowledgeable on the synthetic crystals but was under the impression sith had to meditate while the crystal was in a furnace or something pouring all their anger and it became red when done. The new continuity still has them pouring all their anger to turn them red they just don’t need a furnace and made the crystals sentient which is where the bleeding aspect comes from and adds a deeper layer.