How Did Krillin Get Stronger After Potential Unlock in DBZ? In Dragon Ball Z ep.54, (this is during the Namek Saga), the Elder Guru unlocks 
Krillin's sleeping potential, and so Krillin reaches his full potential, at a power level of 14,000. By the time Krillin fights Goku who was being possessed by Captain Ginyu (ep.71 I believe), he has a power level of 22,000, and by the time the Z fighters fight Android 18 (ep. 135 I believe), Krillin has a power level of 450,000!

If Krillin's true potential was really unlocked way back in the Namek Saga, then how could it have risen, wouldn't that mean that his true potential wasn't really unlocked? His power should have either been as high as it became at the start, or it shouldn't have been able to rise. Is there an in-universe explanation for this?
Well the same could be said about Ultimate Gohan. The Elder Kai basically brought out Gohan's untapped potential. However, the  Ultimate Gohan in the Universal Survival arc is a lot stronger compared to the Ultimate Gohan in the Buu Saga. Even during the course of training, Picollo stated himself that Gohan could get a lot stronger.I believe a good explanation or the way to look at it would be this way. Fighter A is only using 75% of his power X when there is 25% of untapped power. However, the X can be modified by training. A good analogy would be comparing it Cell vs Gohan. Gohan's wasn't using all of his true power while fighting Cell in the start until he tapped into SSJ2. However, SSJ2 wasn't obviously the maximum level of strength Gohan could attain as he grew a lot stronger.