I am the SG in that one. It worked, Inigo countered the Lancea Magica. It really has nothing to do with how powerful the spell is. It is all about speed.
And why, pray-tell why are you stuck on this "must know the Form" bit? Totally different spell. That is for Fast Cast Spontaneous Defenses. This is a Formulaic spell with a specific function, Perdo-Vim, using the more restrictive and more difficult guidline against any magic, regardless of Form. Why do I need to know Form when I am using a spell designed against all forms?
And, that spell as written was presented to Max (the ASG), the entire Novus Mane troupe, and even the Atlas Forums! It was wholeheartedly approved as written, and other characters in the game have now started learning it. In fact, Roberto owes you a season of teaching you that spell whenever you are ready. Fair is fair, you can use it, I can use it, the bad guy can use it, some one can use it to counter your use of it, and so forth and so on.
Original presentation on the Forums:
Presentation to the Novus Mane Troupe:
A Spont PeVi counterspell as a defense against an enemy using a Lancea Magica spell in an attempt to take down the hero's Parma:
And this myth was already debunked earlier, why are you still resorting to it?