It strikes me that the Giant is very consistent in which people can identify spells and which cannot. For instance, in the Order, Roy and Haley appear to be capable of identifying them, whereas Belkar and Elan can't. Gannji does, but Enor doesn't either. Perhaps we can infer something from that.
Added now.
Oceanic, you should probably add this one :)
That's a clear RAW explanation of what happens, then. I don't think that "but The Giant might not use some rule" is a strong argument; the whole point of this thread is to assume that he does follow the rules and see what they might be. You could counter pretty much everything in this thread with the argument "or The Giant might not use that rule", but I really don't see the point in that.
But doesn't every adventurer have a minimum constitution of 3 anyway?
Good catch. The whole business of nemeses aside, in 795 Vaarsuvius outright states that Z is the same level. And Z should be 16, not 13-16, because 860 doesn't tell us whether he's blinded or not, but 862 does.