Originally Posted by
Szar_Lakol
The "IFCC refills" isn't an explanation, and it has zero backing. The fact that a soul splice rejuvenates the subject to full spellcasting capability does not indicate whether or not the Directors can do the same thing at any old time.
V likely levelled to 16 while he was on his own on the Plane of Elemental Ranch Dressing. We know he did at least some adventuring while there. If he levelled to 16, he got a stat increase, which he likely put into Int, increasing it from 23 to 24. It is by far the more reasonable explanation.