Nobility can resurrect in a unique way that has nothing to do with cell regeneration or production at the atomic level. Atomic Blaster, Plasma Cannon, Anti-Proton Missiles....all useless. Even seemingly destroying the body completely they resurrect, completely regenerating their clothes, rings, necklaces etc. even if they are ordinary and have no properties to perpetuated that ability. Only weakness to true sunlight, stakes to the heart, iron based weapons can bypass this ability. Cutting the head off may work if it is kept away from the body long enough.
In many Greater Nobility, they are resistant to these weaknesses.
Gilzen possesses True Immortality which he achieved through science and sorcery, where he is immune completely from all vampire weaknesses, and even the Fountain of Life being severed. He also possesses Reactive Adaptation, further making him harder to kill. If for some reason his reactive adaptation fails he would resurrect at will. Only D's Miracle Blood Light attack can prevent him from resurrecting and destroy his true immortality. A power that may have been given to him by the Sacred Ancestor.
D possesses a seemingly higher level than others with the means to resurrect gaining immunity over time completely from all weaknesses .
The Sacred Ancestor seems to possesses ability that surpasses D in resurrection and could be considered a higher form of resurrection entirely, able to resurrect at will.