The Law, in general, says that vendor has to give you the building with the meters specified in contract, and when that is impossible (lets say a building mistake 🙄 ) you have the right to choose between getting a percentage refund or canceling the contract, but this second option only if the area missing is more than the 10% of the whole surface.
You have the right to choose, not the vendor.
Anyway, sometimes Courts have soften this rule in behalf of the purchaser when they had considered that the missing meters, though smaller than 10% of the whole area, was essential in the house (imagine you have in contract a 200 m2 house, with four bedrooms and the vendor/developer gives you a 182m2 house with only three bedrooms, the area missing -a 18m2 bedroom- is less than the 10% but you wanted four, you would never have bought a three piece house…)
Still think the same about the Catastro Certificate, they get that much data every day, their files take tooooo long to update -sometimes even up to a year- Anyway, the last data in a new built house will come from the Town Hall after the Inspections, the First Occupation License, and updates of the local planning. This last information will be really reliable and maybe the only to trust, bear in mind that all the other data comes simply from the Notario as it has been declared by whom???? yes, the ‘good’ guy of this movie… the developer 😈 .
Catastro information it’s only valid for tax purposes and wont give you the exact number of your house meters as it would include also the percentage you own of the common elements of the building (a house of say 70 m2 could have in the Catastro certificate 100 m2 as you will also own ‘some’ of the hallways, elevators, stairs, etc…)