They do not have access to the pre-existing contract. So they would not be able to confirm anythiong. Also, due to Data Protection, they would not allow them to have access to such information.
Why do you say that? Apple are official agents of O2, just like CPW or any other independent mobile shop that you can get O2 phones from. So they do have access to the O2 contract system (except when it crashes like it surely will do at some point today) and there's no data protection issues whatsoever.