Edit for clarity: This is the closest I was able to find, and is short on details. https://github.com/filecoin-project/specs/blob/master/proofs...
For example, if there is a loophole in "proof of spacetime" then you might be paying for your data to be backed up 8 times and have it only backed up once. You find out that was the case only when that node disappears and your data is lost.
A multi-account attack (sybil?) can just store the file once, and pretend to store it N times, inflating the cost (attacker revenue) by N fold. I can't see how this is avoidable other than being an authority with insight into most of the internet traffic structure. ...Maybe it is designed to only work within china?
last question was a joke, but note that every single multi-account protection requires a breach of anonymity. That's why most modern distributed protocols try to completely work around any benefit of having multiple accounts. Storage, by definition, can't.
P and (the fake) P2 can both reply to V with perfectly normalized storage.
But regardless if the protection works against bad actors, it definitely "works" against good actors if you take into account storage prices. E.g. P1 and P2 are two distinct good actors. They both pay cloudProviderA for storage. P1 and P2 bid on the same filecoin storage contract. They store that independently of each other, but cloudProviderA normalize the storage (with their own backup and consistency solutions). But with this protection scheme, since the cloud provider can't normalize, the cost will eventually go up because their normalization margin got erased. Over time, the data storage cost for good actors will go up, while for bad actors (assuming they are possible) the profit will increase.