Originally Posted by
GregTD
While I don't believe he realizes it, zimmer already shot that down:
"Though on the plus side, the rejuvenating effects of the Soul Splice will allow you to start with all spell slots fully replenished."
We know that V's body was "rejuvenated" to full HP this time. The Soul Splice rejuvenation took less than 20 minutes, and didn't involve V looking at her spell book, or resting.
So, we know that the IFCC can do it, and the restoration of health (that was not promised) shows that V gets benefits from the grab that weren't explained before hand.
So unless you have a good story about how V picked up an extra bit of Int, and an extra level, without anyone really noticing, I'd say the "IFCC refills" is the best explanation.