Unknown Longevity Cost

Suppose a magus was working on a longevity ritual for a mundane man. This man, for whatever reason, lies about his age. The magus brings too few pawns of vis to the ritual.

What happens?

Is the vis consumed?
Does the ritual appear to have worked?
Does it obviously fail?

The vis is a technical requirement for the ritual. So it will become apparent to the magus when he is developing the ritual how much vis he needs.

If he happens to not have enough vis available, for whatever reason, then he can't complete the ritual. The ritual is never performed, the vis is not used, this is apparent and obvious to the magus. In this respect, having too few pawns of vis because the target lied about his age is no different to having too few pawns of vis because someone has stolen the vis in your laboratory. I suppose the magus could try to do the ritual anyway, but it would have no effect, and would waste the vis --- and he would know that it wasn't going to work.

At what point the magus discovers how many pawns of vis are needed is unclear. Does he discover at the end of the season (and so the season is wasted), or does he discover early on, which lets him do something else for the season. I guess that's up to you.

Some sort of relatively trivial InCo effect could probably tell the magus the real age of the target, anyway.

In 4th Ed. This was Intellego Corpus. A magus was supposed to use various InCo magics on his subject so he would know how to brew the potion correctly. This would inevitably reveal such lies.

I think the same is true for 5th ed. You do not just stir togehter some components. You work with the man/woman. The magus will know the true age sooner or later.

If you just toss in too few pawns of vis, the ritual will fail, and the vis will be consumed in the process. Depending on the health of the mundane, the flaw may only be revealed years later.

I imagine that the mage would probably use some sort of rough horroscope in his ritual calculations and probably realise the guy was mistaken very quickly as the sypathies and resonances refused to sync.