Self-disclosure: What is allowed?

Hello everyone,
we have received a self-disclosure form from the bank that may possibly take over our construction financing for the single-family house. However, one question on this self-disclosure form makes me somewhat suspicious: "Account number and bank code at other credit institutions."

Now I am well aware that there is a Federal Data Protection Act and banking secrecy, and I actually don't want to make a big fuss about it, but I would still be interested to know whether this is entirely lawful???

The bank only gets the information that there are other accounts, nothing more, nothing less, and that is legitimate.

I myself have 3 accounts. Until 2 years ago, even 4 because I still had the business account.

The bank only receives the information that there are other accounts

So not the account number itself but only the existence of other accounts. Did I understand that correctly?

Yes, I even believe from loans that are running.

There are no rules about what may or may not be asked, nor whether such information influences a credit decision and whether this data is even stored (long-term). Some information may not be used at all by automated scoring procedures. Other decisions depend on the individual nature of the voter. It can already be enough if the nose is crooked. This is unprofessional, but it can happen.

As a rule, this information (especially for business customers) is used to obtain bank-to-bank inquiries. For private individuals, consent must be given separately anyway. I couldn’t immediately say why I as a credit decision-maker would need such information at all, except for cross-selling.

Counter-question: What advantage do you hope to gain by not providing this information (or providing it incorrectly).

Counter question: What advantage do you hope to gain by not providing this information (or providing it incorrectly).

It's about principle and data protection.