As soon as the buyer receives the tax assessment notice from the tax authorities, he must pay the real estate transfer tax to the state. After notarization of the purchase contract, the tax office is automatically informed. After settling the tax liability, the authority sends a clearance certificate to the notary who notarized the purchase contract. Only then can the entry of the new owner in the land register take place.
One might still assume that an issued real estate transfer tax assessment from the tax office is binding. The question now is whether the tax assessment for your purchase at that time is to be regarded as provisional or final. After all, there was a clearance certificate to the notary, and the purchase contract was thus legally executed and entered in the land register.
In this respect, the question arises whether the tax office can still change the assessment at that time and thus justify a supplementary demand. No new tax-related findings have emerged subsequently. The notarized purchase contract was also known to the tax office at that time.