do I have to notify that another insurer rejected us earlier

Previous refusal: no fixed answer from a register

Whether you must report that another insurer has previously rejected you is not laid down in any law or standard that we can point to here — this is a question from the insurer's own acceptance form, not from an external standard. Most acceptance forms ask this question explicitly, and then the answer is factual: has an application ever been refused, rejected or terminated early by another insurer, yes or no. That is not an assessment and not an interpretation, so you enter what actually happened — not what you think the insurer wants to hear.

Where it often goes wrong: people read "refused" too literally and only count an outright rejection. A modified quotation with exclusions, a cancellation, or a policy that the insurer itself has terminated, in practice usually also falls under what is being asked — check the exact wording of the question itself, as that determines the scope, not your own definition of "refusal". If you have no file in which this is recorded, there is also no source on which to base an answer; in that case you reconstruct it from your own policy history, not from an assumption.

Why this does not come from our source list

None of the sources available for this platform — the Trade Register Act 2007, the EFRAG VSME, the CSRD, ISO/IEC 27001 or NIS2 article 21 — regulates an insurer's acceptance question. That is not an omission: insurers ask this on the basis of their own acceptance policy and risk model, not on the basis of a European directive or national law. The question does sometimes touch on data that is recorded, such as the registration number under which the enterprise is registered or the sector in which the enterprise operates — which may be relevant to support the context of a previous refusal, but do not determine whether reporting is mandatory. That follows from the policy terms and the application form of the insurer asking the question.