Quest state, inventory and the particular monster all matter.
The reviewed quest requires Enhance Your Weapon to be started and exactly one recognized Soul Crystal inventory entry. Multiple recognized entries invalidate crystal selection. The monster must have an entry for the crystal's current stage; a stage listing is not automatically the final awarded stage.
Absorption rules distinguish last-hit and party leveling; eligible members and the monster's stage/chance data matter. Use the Soul Crystal tool for the selected NPC instead of treating all bosses as guaranteed upgrades.