The notary also has to deposit a copy of the contract. He is only allowed to make this copy of the original signed document after a stamp of registration has been put on that original contract.
The deposit of these documents means the legal start of the existance of the company.
The summery made by the notary is published in the Official Belgian Gazette, but this part is only publihed on the internet. The summery contains standard information which might be of importance to third persons, e.g. the representation of the company.