Final Fantasy XII The Zodiac Age - How to farm Dustia to Level Up Quickly from Early On

From within the comments section to the above video:

takahara maragara:

Will Dustia re-spawn if you kill it and don't change screens?

Auster:

No. Why? Because the game registers that you killed it when the EXP and AP points fully appear on the screen. If you exit the area before these points appear, the game gets in a weird state where you receive the points but the game doesn't know that you killed it, meaning that you can keep chaining it.