All the vaults of a section will have, more or less, the same amount of data because the data is distributed randomly through the XOR space and each data is copied into the Vaults closest to their own XOR address. Only when a Vault is surrounded by saturated nodes will store relocated chunks. This makes a multi TB array Vault, usually, totally oversized and economically inefficient.
We must never trust what a vault declares, only the work it can prove. We can use a proof of storage but, in any case, the ideal is to confirm that a Vault has the necessary space but not reward those who have surplus storage.