Even in case of the material non-appealability of an Inheritance and Gift Tax assessment notice, the acquirer can apply (irrevocably) for the optional relief (100% tax exemption) if due to an amended determination of § 151 para. 1 no. 2, 3 Valuation Act the ratio of the non-operating assets to the fair market value of the company or the transferred interest in a partnership/share in a corporation does not exceed 10% for the very first time. Therefore, the amendment (§ 175 para. 1 sent. 1 no. 1 General Fiscal Code) comprises the possibility to apply for the optional relief.
In many cases the acquirer is not willing to apply for the optional relief immediately since the minimum total payroll and holding regulations are much stricter than in case of the regular relief (85% tax exemption). If the Inheritance and Gift Tax assessment notice is subject to re-examination (§ 164 General Fiscal Code), the optional relief can still be applied for at a later point in time. Otherwise, the acquirer has to decide within one month after the tax assessment notice was announced if he applies for the optional relief or not. In the latter case, an application is not feasible anymore unless the aforementioned event of the Regional Office of Finance (Bavaria) is at hand.
For more details regarding the application for the optional relief see Koeniger, The German Inheritance and Gift Tax, 2017, p. 201 et seqq.